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e75bcd48e2
Now that ->nocb_timer and ->nocb_bypass_timer have become quite similar, this commit merges them together. A new RCU_NOCB_WAKE_BYPASS wake level is introduced. As a result, timers perform all kinds of deferred wake ups but other deferred wakeup callsites only handle non-bypass wakeups in order not to wake up rcuo too early. The timer also unconditionally executes a full barrier so as to order timer_pending() and callback enqueue although the path performing RCU_NOCB_WAKE_FORCE that makes use of it is debatable. It should also test against the rdp leader instead of the current rdp. This unconditional full barrier shouldn't bring visible overhead since these timers almost never fire. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
3016 lines
93 KiB
C
3016 lines
93 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* Copyright Red Hat, 2009
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* Copyright IBM Corporation, 2009
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.ibm.com>
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*/
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#include "../locking/rtmutex_common.h"
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#ifdef CONFIG_RCU_NOCB_CPU
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static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
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static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
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static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp)
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{
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return lockdep_is_held(&rdp->nocb_lock);
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}
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static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
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{
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/* Race on early boot between thread creation and assignment */
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if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread)
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return true;
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if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread)
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if (in_task())
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return true;
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return false;
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}
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#else
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static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp)
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{
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return 0;
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}
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static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
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{
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return false;
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}
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
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{
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/*
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* In order to read the offloaded state of an rdp is a safe
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* and stable way and prevent from its value to be changed
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* under us, we must either hold the barrier mutex, the cpu
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* hotplug lock (read or write) or the nocb lock. Local
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* non-preemptible reads are also safe. NOCB kthreads and
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* timers have their own means of synchronization against the
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* offloaded state updaters.
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*/
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RCU_LOCKDEP_WARN(
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!(lockdep_is_held(&rcu_state.barrier_mutex) ||
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(IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
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rcu_lockdep_is_held_nocb(rdp) ||
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(rdp == this_cpu_ptr(&rcu_data) &&
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!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) ||
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rcu_current_is_nocb_kthread(rdp)),
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"Unsafe read of RCU_NOCB offloaded state"
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);
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return rcu_segcblist_is_offloaded(&rdp->cblist);
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}
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/*
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* Check the RCU kernel configuration parameters and print informative
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* messages about anything out of the ordinary.
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*/
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static void __init rcu_bootup_announce_oddness(void)
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{
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if (IS_ENABLED(CONFIG_RCU_TRACE))
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pr_info("\tRCU event tracing is enabled.\n");
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if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
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(!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
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pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
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RCU_FANOUT);
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if (rcu_fanout_exact)
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pr_info("\tHierarchical RCU autobalancing is disabled.\n");
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if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
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pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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if (IS_ENABLED(CONFIG_PROVE_RCU))
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pr_info("\tRCU lockdep checking is enabled.\n");
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if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
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pr_info("\tRCU strict (and thus non-scalable) grace periods enabled.\n");
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if (RCU_NUM_LVLS >= 4)
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pr_info("\tFour(or more)-level hierarchy is enabled.\n");
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if (RCU_FANOUT_LEAF != 16)
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pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
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RCU_FANOUT_LEAF);
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if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
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pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
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rcu_fanout_leaf);
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if (nr_cpu_ids != NR_CPUS)
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pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_BOOST
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pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
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kthread_prio, CONFIG_RCU_BOOST_DELAY);
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#endif
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if (blimit != DEFAULT_RCU_BLIMIT)
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pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
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if (qhimark != DEFAULT_RCU_QHIMARK)
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pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
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if (qlowmark != DEFAULT_RCU_QLOMARK)
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pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
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if (qovld != DEFAULT_RCU_QOVLD)
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pr_info("\tBoot-time adjustment of callback overload level to %ld.\n", qovld);
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if (jiffies_till_first_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
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if (jiffies_till_next_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
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if (jiffies_till_sched_qs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
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if (rcu_kick_kthreads)
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pr_info("\tKick kthreads if too-long grace period.\n");
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if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
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pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
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if (gp_preinit_delay)
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pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
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if (gp_init_delay)
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pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
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if (gp_cleanup_delay)
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pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
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if (!use_softirq)
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pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
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if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
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pr_info("\tRCU debug extended QS entry/exit.\n");
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rcupdate_announce_bootup_oddness();
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}
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#ifdef CONFIG_PREEMPT_RCU
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static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
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static void rcu_read_unlock_special(struct task_struct *t);
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/*
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* Tell them what RCU they are running.
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*/
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static void __init rcu_bootup_announce(void)
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{
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pr_info("Preemptible hierarchical RCU implementation.\n");
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rcu_bootup_announce_oddness();
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}
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/* Flags for rcu_preempt_ctxt_queue() decision table. */
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#define RCU_GP_TASKS 0x8
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#define RCU_EXP_TASKS 0x4
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#define RCU_GP_BLKD 0x2
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#define RCU_EXP_BLKD 0x1
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/*
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* Queues a task preempted within an RCU-preempt read-side critical
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* section into the appropriate location within the ->blkd_tasks list,
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* depending on the states of any ongoing normal and expedited grace
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* periods. The ->gp_tasks pointer indicates which element the normal
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* grace period is waiting on (NULL if none), and the ->exp_tasks pointer
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* indicates which element the expedited grace period is waiting on (again,
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* NULL if none). If a grace period is waiting on a given element in the
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* ->blkd_tasks list, it also waits on all subsequent elements. Thus,
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* adding a task to the tail of the list blocks any grace period that is
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* already waiting on one of the elements. In contrast, adding a task
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* to the head of the list won't block any grace period that is already
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* waiting on one of the elements.
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*
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* This queuing is imprecise, and can sometimes make an ongoing grace
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* period wait for a task that is not strictly speaking blocking it.
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* Given the choice, we needlessly block a normal grace period rather than
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* blocking an expedited grace period.
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*
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* Note that an endless sequence of expedited grace periods still cannot
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* indefinitely postpone a normal grace period. Eventually, all of the
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* fixed number of preempted tasks blocking the normal grace period that are
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* not also blocking the expedited grace period will resume and complete
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* their RCU read-side critical sections. At that point, the ->gp_tasks
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* pointer will equal the ->exp_tasks pointer, at which point the end of
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* the corresponding expedited grace period will also be the end of the
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* normal grace period.
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*/
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static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
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__releases(rnp->lock) /* But leaves rrupts disabled. */
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{
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int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
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(rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
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(rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
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(rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
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struct task_struct *t = current;
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raw_lockdep_assert_held_rcu_node(rnp);
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WARN_ON_ONCE(rdp->mynode != rnp);
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WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
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/* RCU better not be waiting on newly onlined CPUs! */
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WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
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rdp->grpmask);
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/*
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* Decide where to queue the newly blocked task. In theory,
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* this could be an if-statement. In practice, when I tried
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* that, it was quite messy.
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*/
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switch (blkd_state) {
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case 0:
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case RCU_EXP_TASKS:
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case RCU_EXP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS:
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case RCU_GP_TASKS + RCU_EXP_TASKS:
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/*
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* Blocking neither GP, or first task blocking the normal
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* GP but not blocking the already-waiting expedited GP.
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* Queue at the head of the list to avoid unnecessarily
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* blocking the already-waiting GPs.
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*/
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list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_BLKD:
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case RCU_GP_BLKD:
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case RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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/*
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* First task arriving that blocks either GP, or first task
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* arriving that blocks the expedited GP (with the normal
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* GP already waiting), or a task arriving that blocks
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* both GPs with both GPs already waiting. Queue at the
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* tail of the list to avoid any GP waiting on any of the
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* already queued tasks that are not blocking it.
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*/
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list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_TASKS + RCU_EXP_BLKD:
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case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
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/*
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* Second or subsequent task blocking the expedited GP.
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* The task either does not block the normal GP, or is the
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* first task blocking the normal GP. Queue just after
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* the first task blocking the expedited GP.
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*/
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list_add(&t->rcu_node_entry, rnp->exp_tasks);
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break;
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case RCU_GP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
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/*
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* Second or subsequent task blocking the normal GP.
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* The task does not block the expedited GP. Queue just
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* after the first task blocking the normal GP.
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*/
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list_add(&t->rcu_node_entry, rnp->gp_tasks);
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break;
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default:
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/* Yet another exercise in excessive paranoia. */
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WARN_ON_ONCE(1);
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break;
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}
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/*
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* We have now queued the task. If it was the first one to
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* block either grace period, update the ->gp_tasks and/or
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* ->exp_tasks pointers, respectively, to reference the newly
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* blocked tasks.
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*/
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if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
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WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);
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WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
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}
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if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
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WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry);
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WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
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!(rnp->qsmask & rdp->grpmask));
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WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
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!(rnp->expmask & rdp->grpmask));
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raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
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/*
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* Report the quiescent state for the expedited GP. This expedited
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* GP should not be able to end until we report, so there should be
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* no need to check for a subsequent expedited GP. (Though we are
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* still in a quiescent state in any case.)
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*/
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if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs)
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rcu_report_exp_rdp(rdp);
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else
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WARN_ON_ONCE(rdp->exp_deferred_qs);
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}
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU.
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* Note that this does not necessarily mean that the task currently running
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* on the CPU is in a quiescent state: Instead, it means that the current
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* grace period need not wait on any RCU read-side critical section that
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* starts later on this CPU. It also means that if the current task is
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* in an RCU read-side critical section, it has already added itself to
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* some leaf rcu_node structure's ->blkd_tasks list. In addition to the
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* current task, there might be any number of other tasks blocked while
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* in an RCU read-side critical section.
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*
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* Callers to this function must disable preemption.
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*/
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static void rcu_qs(void)
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{
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RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
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if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
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trace_rcu_grace_period(TPS("rcu_preempt"),
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__this_cpu_read(rcu_data.gp_seq),
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TPS("cpuqs"));
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__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
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barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
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WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
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}
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}
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/*
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* We have entered the scheduler, and the current task might soon be
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* context-switched away from. If this task is in an RCU read-side
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* critical section, we will no longer be able to rely on the CPU to
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* record that fact, so we enqueue the task on the blkd_tasks list.
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* The task will dequeue itself when it exits the outermost enclosing
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* RCU read-side critical section. Therefore, the current grace period
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* cannot be permitted to complete until the blkd_tasks list entries
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* predating the current grace period drain, in other words, until
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* rnp->gp_tasks becomes NULL.
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*
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* Caller must disable interrupts.
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*/
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void rcu_note_context_switch(bool preempt)
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{
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struct task_struct *t = current;
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struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
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struct rcu_node *rnp;
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trace_rcu_utilization(TPS("Start context switch"));
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lockdep_assert_irqs_disabled();
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WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0);
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if (rcu_preempt_depth() > 0 &&
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!t->rcu_read_unlock_special.b.blocked) {
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/* Possibly blocking in an RCU read-side critical section. */
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rnp = rdp->mynode;
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raw_spin_lock_rcu_node(rnp);
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t->rcu_read_unlock_special.b.blocked = true;
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t->rcu_blocked_node = rnp;
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/*
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* Verify the CPU's sanity, trace the preemption, and
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* then queue the task as required based on the states
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* of any ongoing and expedited grace periods.
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*/
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WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
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WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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trace_rcu_preempt_task(rcu_state.name,
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t->pid,
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(rnp->qsmask & rdp->grpmask)
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? rnp->gp_seq
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: rcu_seq_snap(&rnp->gp_seq));
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rcu_preempt_ctxt_queue(rnp, rdp);
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} else {
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rcu_preempt_deferred_qs(t);
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}
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/*
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* Either we were not in an RCU read-side critical section to
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* begin with, or we have now recorded that critical section
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* globally. Either way, we can now note a quiescent state
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* for this CPU. Again, if we were in an RCU read-side critical
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* section, and if that critical section was blocking the current
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* grace period, then the fact that the task has been enqueued
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* means that we continue to block the current grace period.
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*/
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rcu_qs();
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if (rdp->exp_deferred_qs)
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rcu_report_exp_rdp(rdp);
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rcu_tasks_qs(current, preempt);
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trace_rcu_utilization(TPS("End context switch"));
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}
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EXPORT_SYMBOL_GPL(rcu_note_context_switch);
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/*
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* Check for preempted RCU readers blocking the current grace period
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* for the specified rcu_node structure. If the caller needs a reliable
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* answer, it must hold the rcu_node's ->lock.
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*/
|
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
|
{
|
|
return READ_ONCE(rnp->gp_tasks) != NULL;
|
|
}
|
|
|
|
/* limit value for ->rcu_read_lock_nesting. */
|
|
#define RCU_NEST_PMAX (INT_MAX / 2)
|
|
|
|
static void rcu_preempt_read_enter(void)
|
|
{
|
|
current->rcu_read_lock_nesting++;
|
|
}
|
|
|
|
static int rcu_preempt_read_exit(void)
|
|
{
|
|
return --current->rcu_read_lock_nesting;
|
|
}
|
|
|
|
static void rcu_preempt_depth_set(int val)
|
|
{
|
|
current->rcu_read_lock_nesting = val;
|
|
}
|
|
|
|
/*
|
|
* Preemptible RCU implementation for rcu_read_lock().
|
|
* Just increment ->rcu_read_lock_nesting, shared state will be updated
|
|
* if we block.
|
|
*/
|
|
void __rcu_read_lock(void)
|
|
{
|
|
rcu_preempt_read_enter();
|
|
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
|
|
WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
|
|
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread)
|
|
WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true);
|
|
barrier(); /* critical section after entry code. */
|
|
}
|
|
EXPORT_SYMBOL_GPL(__rcu_read_lock);
|
|
|
|
/*
|
|
* Preemptible RCU implementation for rcu_read_unlock().
|
|
* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
|
|
* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
|
|
* invoke rcu_read_unlock_special() to clean up after a context switch
|
|
* in an RCU read-side critical section and other special cases.
|
|
*/
|
|
void __rcu_read_unlock(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
barrier(); // critical section before exit code.
|
|
if (rcu_preempt_read_exit() == 0) {
|
|
barrier(); // critical-section exit before .s check.
|
|
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
|
|
rcu_read_unlock_special(t);
|
|
}
|
|
if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
|
|
int rrln = rcu_preempt_depth();
|
|
|
|
WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX);
|
|
}
|
|
}
|
|
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
|
|
|
|
/*
|
|
* Advance a ->blkd_tasks-list pointer to the next entry, instead
|
|
* returning NULL if at the end of the list.
|
|
*/
|
|
static struct list_head *rcu_next_node_entry(struct task_struct *t,
|
|
struct rcu_node *rnp)
|
|
{
|
|
struct list_head *np;
|
|
|
|
np = t->rcu_node_entry.next;
|
|
if (np == &rnp->blkd_tasks)
|
|
np = NULL;
|
|
return np;
|
|
}
|
|
|
|
/*
|
|
* Return true if the specified rcu_node structure has tasks that were
|
|
* preempted within an RCU read-side critical section.
|
|
*/
|
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
|
{
|
|
return !list_empty(&rnp->blkd_tasks);
|
|
}
|
|
|
|
/*
|
|
* Report deferred quiescent states. The deferral time can
|
|
* be quite short, for example, in the case of the call from
|
|
* rcu_read_unlock_special().
|
|
*/
|
|
static void
|
|
rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
|
|
{
|
|
bool empty_exp;
|
|
bool empty_norm;
|
|
bool empty_exp_now;
|
|
struct list_head *np;
|
|
bool drop_boost_mutex = false;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp;
|
|
union rcu_special special;
|
|
|
|
/*
|
|
* If RCU core is waiting for this CPU to exit its critical section,
|
|
* report the fact that it has exited. Because irqs are disabled,
|
|
* t->rcu_read_unlock_special cannot change.
|
|
*/
|
|
special = t->rcu_read_unlock_special;
|
|
rdp = this_cpu_ptr(&rcu_data);
|
|
if (!special.s && !rdp->exp_deferred_qs) {
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
t->rcu_read_unlock_special.s = 0;
|
|
if (special.b.need_qs) {
|
|
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
|
|
rcu_report_qs_rdp(rdp);
|
|
udelay(rcu_unlock_delay);
|
|
} else {
|
|
rcu_qs();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Respond to a request by an expedited grace period for a
|
|
* quiescent state from this CPU. Note that requests from
|
|
* tasks are handled when removing the task from the
|
|
* blocked-tasks list below.
|
|
*/
|
|
if (rdp->exp_deferred_qs)
|
|
rcu_report_exp_rdp(rdp);
|
|
|
|
/* Clean up if blocked during RCU read-side critical section. */
|
|
if (special.b.blocked) {
|
|
|
|
/*
|
|
* Remove this task from the list it blocked on. The task
|
|
* now remains queued on the rcu_node corresponding to the
|
|
* CPU it first blocked on, so there is no longer any need
|
|
* to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
|
|
*/
|
|
rnp = t->rcu_blocked_node;
|
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
|
WARN_ON_ONCE(rnp != t->rcu_blocked_node);
|
|
WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
|
|
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
|
|
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
|
|
(!empty_norm || rnp->qsmask));
|
|
empty_exp = sync_rcu_exp_done(rnp);
|
|
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
|
|
np = rcu_next_node_entry(t, rnp);
|
|
list_del_init(&t->rcu_node_entry);
|
|
t->rcu_blocked_node = NULL;
|
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
|
|
rnp->gp_seq, t->pid);
|
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
|
WRITE_ONCE(rnp->gp_tasks, np);
|
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
|
WRITE_ONCE(rnp->exp_tasks, np);
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST)) {
|
|
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
|
|
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
|
|
if (&t->rcu_node_entry == rnp->boost_tasks)
|
|
WRITE_ONCE(rnp->boost_tasks, np);
|
|
}
|
|
|
|
/*
|
|
* If this was the last task on the current list, and if
|
|
* we aren't waiting on any CPUs, report the quiescent state.
|
|
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
|
|
* so we must take a snapshot of the expedited state.
|
|
*/
|
|
empty_exp_now = sync_rcu_exp_done(rnp);
|
|
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
|
|
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
|
|
rnp->gp_seq,
|
|
0, rnp->qsmask,
|
|
rnp->level,
|
|
rnp->grplo,
|
|
rnp->grphi,
|
|
!!rnp->gp_tasks);
|
|
rcu_report_unblock_qs_rnp(rnp, flags);
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
/* Unboost if we were boosted. */
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
|
|
rt_mutex_futex_unlock(&rnp->boost_mtx);
|
|
|
|
/*
|
|
* If this was the last task on the expedited lists,
|
|
* then we need to report up the rcu_node hierarchy.
|
|
*/
|
|
if (!empty_exp && empty_exp_now)
|
|
rcu_report_exp_rnp(rnp, true);
|
|
} else {
|
|
local_irq_restore(flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Is a deferred quiescent-state pending, and are we also not in
|
|
* an RCU read-side critical section? It is the caller's responsibility
|
|
* to ensure it is otherwise safe to report any deferred quiescent
|
|
* states. The reason for this is that it is safe to report a
|
|
* quiescent state during context switch even though preemption
|
|
* is disabled. This function cannot be expected to understand these
|
|
* nuances, so the caller must handle them.
|
|
*/
|
|
static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
|
|
{
|
|
return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
|
|
READ_ONCE(t->rcu_read_unlock_special.s)) &&
|
|
rcu_preempt_depth() == 0;
|
|
}
|
|
|
|
/*
|
|
* Report a deferred quiescent state if needed and safe to do so.
|
|
* As with rcu_preempt_need_deferred_qs(), "safe" involves only
|
|
* not being in an RCU read-side critical section. The caller must
|
|
* evaluate safety in terms of interrupt, softirq, and preemption
|
|
* disabling.
|
|
*/
|
|
static void rcu_preempt_deferred_qs(struct task_struct *t)
|
|
{
|
|
unsigned long flags;
|
|
|
|
if (!rcu_preempt_need_deferred_qs(t))
|
|
return;
|
|
local_irq_save(flags);
|
|
rcu_preempt_deferred_qs_irqrestore(t, flags);
|
|
}
|
|
|
|
/*
|
|
* Minimal handler to give the scheduler a chance to re-evaluate.
|
|
*/
|
|
static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
|
|
{
|
|
struct rcu_data *rdp;
|
|
|
|
rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
|
|
rdp->defer_qs_iw_pending = false;
|
|
}
|
|
|
|
/*
|
|
* Handle special cases during rcu_read_unlock(), such as needing to
|
|
* notify RCU core processing or task having blocked during the RCU
|
|
* read-side critical section.
|
|
*/
|
|
static void rcu_read_unlock_special(struct task_struct *t)
|
|
{
|
|
unsigned long flags;
|
|
bool irqs_were_disabled;
|
|
bool preempt_bh_were_disabled =
|
|
!!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
|
|
|
|
/* NMI handlers cannot block and cannot safely manipulate state. */
|
|
if (in_nmi())
|
|
return;
|
|
|
|
local_irq_save(flags);
|
|
irqs_were_disabled = irqs_disabled_flags(flags);
|
|
if (preempt_bh_were_disabled || irqs_were_disabled) {
|
|
bool expboost; // Expedited GP in flight or possible boosting.
|
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) ||
|
|
(rdp->grpmask & READ_ONCE(rnp->expmask)) ||
|
|
IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
|
|
(IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled &&
|
|
t->rcu_blocked_node);
|
|
// Need to defer quiescent state until everything is enabled.
|
|
if (use_softirq && (in_irq() || (expboost && !irqs_were_disabled))) {
|
|
// Using softirq, safe to awaken, and either the
|
|
// wakeup is free or there is either an expedited
|
|
// GP in flight or a potential need to deboost.
|
|
raise_softirq_irqoff(RCU_SOFTIRQ);
|
|
} else {
|
|
// Enabling BH or preempt does reschedule, so...
|
|
// Also if no expediting and no possible deboosting,
|
|
// slow is OK. Plus nohz_full CPUs eventually get
|
|
// tick enabled.
|
|
set_tsk_need_resched(current);
|
|
set_preempt_need_resched();
|
|
if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
|
|
expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
|
|
// Get scheduler to re-evaluate and call hooks.
|
|
// If !IRQ_WORK, FQS scan will eventually IPI.
|
|
init_irq_work(&rdp->defer_qs_iw, rcu_preempt_deferred_qs_handler);
|
|
rdp->defer_qs_iw_pending = true;
|
|
irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
|
|
}
|
|
}
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
rcu_preempt_deferred_qs_irqrestore(t, flags);
|
|
}
|
|
|
|
/*
|
|
* Check that the list of blocked tasks for the newly completed grace
|
|
* period is in fact empty. It is a serious bug to complete a grace
|
|
* period that still has RCU readers blocked! This function must be
|
|
* invoked -before- updating this rnp's ->gp_seq.
|
|
*
|
|
* Also, if there are blocked tasks on the list, they automatically
|
|
* block the newly created grace period, so set up ->gp_tasks accordingly.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
|
|
raw_lockdep_assert_held_rcu_node(rnp);
|
|
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
|
|
dump_blkd_tasks(rnp, 10);
|
|
if (rcu_preempt_has_tasks(rnp) &&
|
|
(rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
|
|
WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
|
|
t = container_of(rnp->gp_tasks, struct task_struct,
|
|
rcu_node_entry);
|
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
|
|
rnp->gp_seq, t->pid);
|
|
}
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
/*
|
|
* Check for a quiescent state from the current CPU, including voluntary
|
|
* context switches for Tasks RCU. When a task blocks, the task is
|
|
* recorded in the corresponding CPU's rcu_node structure, which is checked
|
|
* elsewhere, hence this function need only check for quiescent states
|
|
* related to the current CPU, not to those related to tasks.
|
|
*/
|
|
static void rcu_flavor_sched_clock_irq(int user)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
if (user || rcu_is_cpu_rrupt_from_idle()) {
|
|
rcu_note_voluntary_context_switch(current);
|
|
}
|
|
if (rcu_preempt_depth() > 0 ||
|
|
(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
|
|
/* No QS, force context switch if deferred. */
|
|
if (rcu_preempt_need_deferred_qs(t)) {
|
|
set_tsk_need_resched(t);
|
|
set_preempt_need_resched();
|
|
}
|
|
} else if (rcu_preempt_need_deferred_qs(t)) {
|
|
rcu_preempt_deferred_qs(t); /* Report deferred QS. */
|
|
return;
|
|
} else if (!WARN_ON_ONCE(rcu_preempt_depth())) {
|
|
rcu_qs(); /* Report immediate QS. */
|
|
return;
|
|
}
|
|
|
|
/* If GP is oldish, ask for help from rcu_read_unlock_special(). */
|
|
if (rcu_preempt_depth() > 0 &&
|
|
__this_cpu_read(rcu_data.core_needs_qs) &&
|
|
__this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
|
|
!t->rcu_read_unlock_special.b.need_qs &&
|
|
time_after(jiffies, rcu_state.gp_start + HZ))
|
|
t->rcu_read_unlock_special.b.need_qs = true;
|
|
}
|
|
|
|
/*
|
|
* Check for a task exiting while in a preemptible-RCU read-side
|
|
* critical section, clean up if so. No need to issue warnings, as
|
|
* debug_check_no_locks_held() already does this if lockdep is enabled.
|
|
* Besides, if this function does anything other than just immediately
|
|
* return, there was a bug of some sort. Spewing warnings from this
|
|
* function is like as not to simply obscure important prior warnings.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (unlikely(!list_empty(¤t->rcu_node_entry))) {
|
|
rcu_preempt_depth_set(1);
|
|
barrier();
|
|
WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
|
|
} else if (unlikely(rcu_preempt_depth())) {
|
|
rcu_preempt_depth_set(1);
|
|
} else {
|
|
return;
|
|
}
|
|
__rcu_read_unlock();
|
|
rcu_preempt_deferred_qs(current);
|
|
}
|
|
|
|
/*
|
|
* Dump the blocked-tasks state, but limit the list dump to the
|
|
* specified number of elements.
|
|
*/
|
|
static void
|
|
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
|
|
{
|
|
int cpu;
|
|
int i;
|
|
struct list_head *lhp;
|
|
bool onl;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp1;
|
|
|
|
raw_lockdep_assert_held_rcu_node(rnp);
|
|
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
|
|
__func__, rnp->grplo, rnp->grphi, rnp->level,
|
|
(long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs);
|
|
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
|
|
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
|
|
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
|
|
pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
|
|
__func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
|
|
READ_ONCE(rnp->exp_tasks));
|
|
pr_info("%s: ->blkd_tasks", __func__);
|
|
i = 0;
|
|
list_for_each(lhp, &rnp->blkd_tasks) {
|
|
pr_cont(" %p", lhp);
|
|
if (++i >= ncheck)
|
|
break;
|
|
}
|
|
pr_cont("\n");
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
|
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
|
|
pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
|
|
cpu, ".o"[onl],
|
|
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
|
|
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
|
|
}
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
/*
|
|
* If strict grace periods are enabled, and if the calling
|
|
* __rcu_read_unlock() marks the beginning of a quiescent state, immediately
|
|
* report that quiescent state and, if requested, spin for a bit.
|
|
*/
|
|
void rcu_read_unlock_strict(void)
|
|
{
|
|
struct rcu_data *rdp;
|
|
|
|
if (!IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ||
|
|
irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
|
|
return;
|
|
rdp = this_cpu_ptr(&rcu_data);
|
|
rcu_report_qs_rdp(rdp);
|
|
udelay(rcu_unlock_delay);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_read_unlock_strict);
|
|
|
|
/*
|
|
* Tell them what RCU they are running.
|
|
*/
|
|
static void __init rcu_bootup_announce(void)
|
|
{
|
|
pr_info("Hierarchical RCU implementation.\n");
|
|
rcu_bootup_announce_oddness();
|
|
}
|
|
|
|
/*
|
|
* Note a quiescent state for PREEMPTION=n. Because we do not need to know
|
|
* how many quiescent states passed, just if there was at least one since
|
|
* the start of the grace period, this just sets a flag. The caller must
|
|
* have disabled preemption.
|
|
*/
|
|
static void rcu_qs(void)
|
|
{
|
|
RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
|
|
if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
|
|
return;
|
|
trace_rcu_grace_period(TPS("rcu_sched"),
|
|
__this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
|
|
__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
|
|
if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
|
|
return;
|
|
__this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
|
|
rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
|
|
}
|
|
|
|
/*
|
|
* Register an urgently needed quiescent state. If there is an
|
|
* emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
|
|
* dyntick-idle quiescent state visible to other CPUs, which will in
|
|
* some cases serve for expedited as well as normal grace periods.
|
|
* Either way, register a lightweight quiescent state.
|
|
*/
|
|
void rcu_all_qs(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
|
|
return;
|
|
preempt_disable();
|
|
/* Load rcu_urgent_qs before other flags. */
|
|
if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
|
|
preempt_enable();
|
|
return;
|
|
}
|
|
this_cpu_write(rcu_data.rcu_urgent_qs, false);
|
|
if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
|
|
local_irq_save(flags);
|
|
rcu_momentary_dyntick_idle();
|
|
local_irq_restore(flags);
|
|
}
|
|
rcu_qs();
|
|
preempt_enable();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_all_qs);
|
|
|
|
/*
|
|
* Note a PREEMPTION=n context switch. The caller must have disabled interrupts.
|
|
*/
|
|
void rcu_note_context_switch(bool preempt)
|
|
{
|
|
trace_rcu_utilization(TPS("Start context switch"));
|
|
rcu_qs();
|
|
/* Load rcu_urgent_qs before other flags. */
|
|
if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
|
|
goto out;
|
|
this_cpu_write(rcu_data.rcu_urgent_qs, false);
|
|
if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
|
|
rcu_momentary_dyntick_idle();
|
|
rcu_tasks_qs(current, preempt);
|
|
out:
|
|
trace_rcu_utilization(TPS("End context switch"));
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there are never any preempted
|
|
* RCU readers.
|
|
*/
|
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked.
|
|
*/
|
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no deferred quiescent
|
|
* states.
|
|
*/
|
|
static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
|
|
{
|
|
return false;
|
|
}
|
|
static void rcu_preempt_deferred_qs(struct task_struct *t) { }
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked,
|
|
* so there is no need to check for blocked tasks. So check only for
|
|
* bogus qsmask values.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
/*
|
|
* Check to see if this CPU is in a non-context-switch quiescent state,
|
|
* namely user mode and idle loop.
|
|
*/
|
|
static void rcu_flavor_sched_clock_irq(int user)
|
|
{
|
|
if (user || rcu_is_cpu_rrupt_from_idle()) {
|
|
|
|
/*
|
|
* Get here if this CPU took its interrupt from user
|
|
* mode or from the idle loop, and if this is not a
|
|
* nested interrupt. In this case, the CPU is in
|
|
* a quiescent state, so note it.
|
|
*
|
|
* No memory barrier is required here because rcu_qs()
|
|
* references only CPU-local variables that other CPUs
|
|
* neither access nor modify, at least not while the
|
|
* corresponding CPU is online.
|
|
*/
|
|
|
|
rcu_qs();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, tasks cannot possibly exit
|
|
* while in preemptible RCU read-side critical sections.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Dump the guaranteed-empty blocked-tasks state. Trust but verify.
|
|
*/
|
|
static void
|
|
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
|
|
{
|
|
WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
/*
|
|
* If boosting, set rcuc kthreads to realtime priority.
|
|
*/
|
|
static void rcu_cpu_kthread_setup(unsigned int cpu)
|
|
{
|
|
#ifdef CONFIG_RCU_BOOST
|
|
struct sched_param sp;
|
|
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
/*
|
|
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
|
|
* or ->boost_tasks, advancing the pointer to the next task in the
|
|
* ->blkd_tasks list.
|
|
*
|
|
* Note that irqs must be enabled: boosting the task can block.
|
|
* Returns 1 if there are more tasks needing to be boosted.
|
|
*/
|
|
static int rcu_boost(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct task_struct *t;
|
|
struct list_head *tb;
|
|
|
|
if (READ_ONCE(rnp->exp_tasks) == NULL &&
|
|
READ_ONCE(rnp->boost_tasks) == NULL)
|
|
return 0; /* Nothing left to boost. */
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
|
|
/*
|
|
* Recheck under the lock: all tasks in need of boosting
|
|
* might exit their RCU read-side critical sections on their own.
|
|
*/
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Preferentially boost tasks blocking expedited grace periods.
|
|
* This cannot starve the normal grace periods because a second
|
|
* expedited grace period must boost all blocked tasks, including
|
|
* those blocking the pre-existing normal grace period.
|
|
*/
|
|
if (rnp->exp_tasks != NULL)
|
|
tb = rnp->exp_tasks;
|
|
else
|
|
tb = rnp->boost_tasks;
|
|
|
|
/*
|
|
* We boost task t by manufacturing an rt_mutex that appears to
|
|
* be held by task t. We leave a pointer to that rt_mutex where
|
|
* task t can find it, and task t will release the mutex when it
|
|
* exits its outermost RCU read-side critical section. Then
|
|
* simply acquiring this artificial rt_mutex will boost task
|
|
* t's priority. (Thanks to tglx for suggesting this approach!)
|
|
*
|
|
* Note that task t must acquire rnp->lock to remove itself from
|
|
* the ->blkd_tasks list, which it will do from exit() if from
|
|
* nowhere else. We therefore are guaranteed that task t will
|
|
* stay around at least until we drop rnp->lock. Note that
|
|
* rnp->lock also resolves races between our priority boosting
|
|
* and task t's exiting its outermost RCU read-side critical
|
|
* section.
|
|
*/
|
|
t = container_of(tb, struct task_struct, rcu_node_entry);
|
|
rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
/* Lock only for side effect: boosts task t's priority. */
|
|
rt_mutex_lock(&rnp->boost_mtx);
|
|
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
|
|
|
|
return READ_ONCE(rnp->exp_tasks) != NULL ||
|
|
READ_ONCE(rnp->boost_tasks) != NULL;
|
|
}
|
|
|
|
/*
|
|
* Priority-boosting kthread, one per leaf rcu_node.
|
|
*/
|
|
static int rcu_boost_kthread(void *arg)
|
|
{
|
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
|
int spincnt = 0;
|
|
int more2boost;
|
|
|
|
trace_rcu_utilization(TPS("Start boost kthread@init"));
|
|
for (;;) {
|
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
|
|
rcu_wait(READ_ONCE(rnp->boost_tasks) ||
|
|
READ_ONCE(rnp->exp_tasks));
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
|
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
|
|
more2boost = rcu_boost(rnp);
|
|
if (more2boost)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
|
|
schedule_timeout_idle(2);
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
|
|
spincnt = 0;
|
|
}
|
|
}
|
|
/* NOTREACHED */
|
|
trace_rcu_utilization(TPS("End boost kthread@notreached"));
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Check to see if it is time to start boosting RCU readers that are
|
|
* blocking the current grace period, and, if so, tell the per-rcu_node
|
|
* kthread to start boosting them. If there is an expedited grace
|
|
* period in progress, it is always time to boost.
|
|
*
|
|
* The caller must hold rnp->lock, which this function releases.
|
|
* The ->boost_kthread_task is immortal, so we don't need to worry
|
|
* about it going away.
|
|
*/
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
__releases(rnp->lock)
|
|
{
|
|
raw_lockdep_assert_held_rcu_node(rnp);
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return;
|
|
}
|
|
if (rnp->exp_tasks != NULL ||
|
|
(rnp->gp_tasks != NULL &&
|
|
rnp->boost_tasks == NULL &&
|
|
rnp->qsmask == 0 &&
|
|
(!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) {
|
|
if (rnp->exp_tasks == NULL)
|
|
WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
rcu_wake_cond(rnp->boost_kthread_task,
|
|
READ_ONCE(rnp->boost_kthread_status));
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Is the current CPU running the RCU-callbacks kthread?
|
|
* Caller must have preemption disabled.
|
|
*/
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
|
|
}
|
|
|
|
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
|
|
|
|
/*
|
|
* Do priority-boost accounting for the start of a new grace period.
|
|
*/
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
|
|
}
|
|
|
|
/*
|
|
* Create an RCU-boost kthread for the specified node if one does not
|
|
* already exist. We only create this kthread for preemptible RCU.
|
|
* Returns zero if all is well, a negated errno otherwise.
|
|
*/
|
|
static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
|
|
{
|
|
int rnp_index = rnp - rcu_get_root();
|
|
unsigned long flags;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
|
|
return;
|
|
|
|
if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
|
|
return;
|
|
|
|
rcu_state.boost = 1;
|
|
|
|
if (rnp->boost_kthread_task != NULL)
|
|
return;
|
|
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
|
"rcub/%d", rnp_index);
|
|
if (WARN_ON_ONCE(IS_ERR(t)))
|
|
return;
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
rnp->boost_kthread_task = t;
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
}
|
|
|
|
/*
|
|
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
|
* served by the rcu_node in question. The CPU hotplug lock is still
|
|
* held, so the value of rnp->qsmaskinit will be stable.
|
|
*
|
|
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
|
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
|
* this function allows the kthread to execute on any CPU.
|
|
*/
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
struct task_struct *t = rnp->boost_kthread_task;
|
|
unsigned long mask = rcu_rnp_online_cpus(rnp);
|
|
cpumask_var_t cm;
|
|
int cpu;
|
|
|
|
if (!t)
|
|
return;
|
|
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
|
return;
|
|
for_each_leaf_node_possible_cpu(rnp, cpu)
|
|
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
|
|
cpu != outgoingcpu)
|
|
cpumask_set_cpu(cpu, cm);
|
|
if (cpumask_weight(cm) == 0)
|
|
cpumask_setall(cm);
|
|
set_cpus_allowed_ptr(t, cm);
|
|
free_cpumask_var(cm);
|
|
}
|
|
|
|
/*
|
|
* Spawn boost kthreads -- called as soon as the scheduler is running.
|
|
*/
|
|
static void __init rcu_spawn_boost_kthreads(void)
|
|
{
|
|
struct rcu_node *rnp;
|
|
|
|
rcu_for_each_leaf_node(rnp)
|
|
rcu_spawn_one_boost_kthread(rnp);
|
|
}
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
|
|
if (rcu_scheduler_fully_active)
|
|
rcu_spawn_one_boost_kthread(rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
__releases(rnp->lock)
|
|
{
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_boost_kthreads(void)
|
|
{
|
|
}
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
#if !defined(CONFIG_RCU_FAST_NO_HZ)
|
|
|
|
/*
|
|
* Check to see if any future non-offloaded RCU-related work will need
|
|
* to be done by the current CPU, even if none need be done immediately,
|
|
* returning 1 if so. This function is part of the RCU implementation;
|
|
* it is -not- an exported member of the RCU API.
|
|
*
|
|
* Because we not have RCU_FAST_NO_HZ, just check whether or not this
|
|
* CPU has RCU callbacks queued.
|
|
*/
|
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
|
{
|
|
*nextevt = KTIME_MAX;
|
|
return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
|
|
!rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
|
|
* after it.
|
|
*/
|
|
static void rcu_cleanup_after_idle(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
|
|
* is nothing.
|
|
*/
|
|
static void rcu_prepare_for_idle(void)
|
|
{
|
|
}
|
|
|
|
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
/*
|
|
* This code is invoked when a CPU goes idle, at which point we want
|
|
* to have the CPU do everything required for RCU so that it can enter
|
|
* the energy-efficient dyntick-idle mode.
|
|
*
|
|
* The following preprocessor symbol controls this:
|
|
*
|
|
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
|
|
* to sleep in dyntick-idle mode with RCU callbacks pending. This
|
|
* is sized to be roughly one RCU grace period. Those energy-efficiency
|
|
* benchmarkers who might otherwise be tempted to set this to a large
|
|
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
|
|
* system. And if you are -that- concerned about energy efficiency,
|
|
* just power the system down and be done with it!
|
|
*
|
|
* The value below works well in practice. If future workloads require
|
|
* adjustment, they can be converted into kernel config parameters, though
|
|
* making the state machine smarter might be a better option.
|
|
*/
|
|
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
|
|
|
|
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
|
|
module_param(rcu_idle_gp_delay, int, 0644);
|
|
|
|
/*
|
|
* Try to advance callbacks on the current CPU, but only if it has been
|
|
* awhile since the last time we did so. Afterwards, if there are any
|
|
* callbacks ready for immediate invocation, return true.
|
|
*/
|
|
static bool __maybe_unused rcu_try_advance_all_cbs(void)
|
|
{
|
|
bool cbs_ready = false;
|
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
struct rcu_node *rnp;
|
|
|
|
/* Exit early if we advanced recently. */
|
|
if (jiffies == rdp->last_advance_all)
|
|
return false;
|
|
rdp->last_advance_all = jiffies;
|
|
|
|
rnp = rdp->mynode;
|
|
|
|
/*
|
|
* Don't bother checking unless a grace period has
|
|
* completed since we last checked and there are
|
|
* callbacks not yet ready to invoke.
|
|
*/
|
|
if ((rcu_seq_completed_gp(rdp->gp_seq,
|
|
rcu_seq_current(&rnp->gp_seq)) ||
|
|
unlikely(READ_ONCE(rdp->gpwrap))) &&
|
|
rcu_segcblist_pend_cbs(&rdp->cblist))
|
|
note_gp_changes(rdp);
|
|
|
|
if (rcu_segcblist_ready_cbs(&rdp->cblist))
|
|
cbs_ready = true;
|
|
return cbs_ready;
|
|
}
|
|
|
|
/*
|
|
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
|
|
* to invoke. If the CPU has callbacks, try to advance them. Tell the
|
|
* caller about what to set the timeout.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
|
{
|
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
unsigned long dj;
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
|
|
/* If no non-offloaded callbacks, RCU doesn't need the CPU. */
|
|
if (rcu_segcblist_empty(&rdp->cblist) ||
|
|
rcu_rdp_is_offloaded(rdp)) {
|
|
*nextevt = KTIME_MAX;
|
|
return 0;
|
|
}
|
|
|
|
/* Attempt to advance callbacks. */
|
|
if (rcu_try_advance_all_cbs()) {
|
|
/* Some ready to invoke, so initiate later invocation. */
|
|
invoke_rcu_core();
|
|
return 1;
|
|
}
|
|
rdp->last_accelerate = jiffies;
|
|
|
|
/* Request timer and round. */
|
|
dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - jiffies;
|
|
|
|
*nextevt = basemono + dj * TICK_NSEC;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Prepare a CPU for idle from an RCU perspective. The first major task is to
|
|
* sense whether nohz mode has been enabled or disabled via sysfs. The second
|
|
* major task is to accelerate (that is, assign grace-period numbers to) any
|
|
* recently arrived callbacks.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_prepare_for_idle(void)
|
|
{
|
|
bool needwake;
|
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
struct rcu_node *rnp;
|
|
int tne;
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
if (rcu_rdp_is_offloaded(rdp))
|
|
return;
|
|
|
|
/* Handle nohz enablement switches conservatively. */
|
|
tne = READ_ONCE(tick_nohz_active);
|
|
if (tne != rdp->tick_nohz_enabled_snap) {
|
|
if (!rcu_segcblist_empty(&rdp->cblist))
|
|
invoke_rcu_core(); /* force nohz to see update. */
|
|
rdp->tick_nohz_enabled_snap = tne;
|
|
return;
|
|
}
|
|
if (!tne)
|
|
return;
|
|
|
|
/*
|
|
* If we have not yet accelerated this jiffy, accelerate all
|
|
* callbacks on this CPU.
|
|
*/
|
|
if (rdp->last_accelerate == jiffies)
|
|
return;
|
|
rdp->last_accelerate = jiffies;
|
|
if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
|
|
rnp = rdp->mynode;
|
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
|
needwake = rcu_accelerate_cbs(rnp, rdp);
|
|
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
|
if (needwake)
|
|
rcu_gp_kthread_wake();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clean up for exit from idle. Attempt to advance callbacks based on
|
|
* any grace periods that elapsed while the CPU was idle, and if any
|
|
* callbacks are now ready to invoke, initiate invocation.
|
|
*/
|
|
static void rcu_cleanup_after_idle(void)
|
|
{
|
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
if (rcu_rdp_is_offloaded(rdp))
|
|
return;
|
|
if (rcu_try_advance_all_cbs())
|
|
invoke_rcu_core();
|
|
}
|
|
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
|
|
/*
|
|
* Offload callback processing from the boot-time-specified set of CPUs
|
|
* specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
|
|
* created that pull the callbacks from the corresponding CPU, wait for
|
|
* a grace period to elapse, and invoke the callbacks. These kthreads
|
|
* are organized into GP kthreads, which manage incoming callbacks, wait for
|
|
* grace periods, and awaken CB kthreads, and the CB kthreads, which only
|
|
* invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
|
|
* do a wake_up() on their GP kthread when they insert a callback into any
|
|
* empty list, unless the rcu_nocb_poll boot parameter has been specified,
|
|
* in which case each kthread actively polls its CPU. (Which isn't so great
|
|
* for energy efficiency, but which does reduce RCU's overhead on that CPU.)
|
|
*
|
|
* This is intended to be used in conjunction with Frederic Weisbecker's
|
|
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
|
|
* running CPU-bound user-mode computations.
|
|
*
|
|
* Offloading of callbacks can also be used as an energy-efficiency
|
|
* measure because CPUs with no RCU callbacks queued are more aggressive
|
|
* about entering dyntick-idle mode.
|
|
*/
|
|
|
|
|
|
/*
|
|
* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
|
|
* If the list is invalid, a warning is emitted and all CPUs are offloaded.
|
|
*/
|
|
static int __init rcu_nocb_setup(char *str)
|
|
{
|
|
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
|
|
if (!strcasecmp(str, "all")) /* legacy: use "0-N" instead */
|
|
cpumask_setall(rcu_nocb_mask);
|
|
else
|
|
if (cpulist_parse(str, rcu_nocb_mask)) {
|
|
pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
|
|
cpumask_setall(rcu_nocb_mask);
|
|
}
|
|
return 1;
|
|
}
|
|
__setup("rcu_nocbs=", rcu_nocb_setup);
|
|
|
|
static int __init parse_rcu_nocb_poll(char *arg)
|
|
{
|
|
rcu_nocb_poll = true;
|
|
return 0;
|
|
}
|
|
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
|
|
|
|
/*
|
|
* Don't bother bypassing ->cblist if the call_rcu() rate is low.
|
|
* After all, the main point of bypassing is to avoid lock contention
|
|
* on ->nocb_lock, which only can happen at high call_rcu() rates.
|
|
*/
|
|
static int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
|
|
module_param(nocb_nobypass_lim_per_jiffy, int, 0);
|
|
|
|
/*
|
|
* Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
|
|
* lock isn't immediately available, increment ->nocb_lock_contended to
|
|
* flag the contention.
|
|
*/
|
|
static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
|
|
__acquires(&rdp->nocb_bypass_lock)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
if (raw_spin_trylock(&rdp->nocb_bypass_lock))
|
|
return;
|
|
atomic_inc(&rdp->nocb_lock_contended);
|
|
WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
|
|
smp_mb__after_atomic(); /* atomic_inc() before lock. */
|
|
raw_spin_lock(&rdp->nocb_bypass_lock);
|
|
smp_mb__before_atomic(); /* atomic_dec() after lock. */
|
|
atomic_dec(&rdp->nocb_lock_contended);
|
|
}
|
|
|
|
/*
|
|
* Spinwait until the specified rcu_data structure's ->nocb_lock is
|
|
* not contended. Please note that this is extremely special-purpose,
|
|
* relying on the fact that at most two kthreads and one CPU contend for
|
|
* this lock, and also that the two kthreads are guaranteed to have frequent
|
|
* grace-period-duration time intervals between successive acquisitions
|
|
* of the lock. This allows us to use an extremely simple throttling
|
|
* mechanism, and further to apply it only to the CPU doing floods of
|
|
* call_rcu() invocations. Don't try this at home!
|
|
*/
|
|
static void rcu_nocb_wait_contended(struct rcu_data *rdp)
|
|
{
|
|
WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
|
|
while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
|
|
cpu_relax();
|
|
}
|
|
|
|
/*
|
|
* Conditionally acquire the specified rcu_data structure's
|
|
* ->nocb_bypass_lock.
|
|
*/
|
|
static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
return raw_spin_trylock(&rdp->nocb_bypass_lock);
|
|
}
|
|
|
|
/*
|
|
* Release the specified rcu_data structure's ->nocb_bypass_lock.
|
|
*/
|
|
static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
|
|
__releases(&rdp->nocb_bypass_lock)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
raw_spin_unlock(&rdp->nocb_bypass_lock);
|
|
}
|
|
|
|
/*
|
|
* Acquire the specified rcu_data structure's ->nocb_lock, but only
|
|
* if it corresponds to a no-CBs CPU.
|
|
*/
|
|
static void rcu_nocb_lock(struct rcu_data *rdp)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
if (!rcu_rdp_is_offloaded(rdp))
|
|
return;
|
|
raw_spin_lock(&rdp->nocb_lock);
|
|
}
|
|
|
|
/*
|
|
* Release the specified rcu_data structure's ->nocb_lock, but only
|
|
* if it corresponds to a no-CBs CPU.
|
|
*/
|
|
static void rcu_nocb_unlock(struct rcu_data *rdp)
|
|
{
|
|
if (rcu_rdp_is_offloaded(rdp)) {
|
|
lockdep_assert_irqs_disabled();
|
|
raw_spin_unlock(&rdp->nocb_lock);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Release the specified rcu_data structure's ->nocb_lock and restore
|
|
* interrupts, but only if it corresponds to a no-CBs CPU.
|
|
*/
|
|
static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
|
|
unsigned long flags)
|
|
{
|
|
if (rcu_rdp_is_offloaded(rdp)) {
|
|
lockdep_assert_irqs_disabled();
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
} else {
|
|
local_irq_restore(flags);
|
|
}
|
|
}
|
|
|
|
/* Lockdep check that ->cblist may be safely accessed. */
|
|
static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
if (rcu_rdp_is_offloaded(rdp))
|
|
lockdep_assert_held(&rdp->nocb_lock);
|
|
}
|
|
|
|
/*
|
|
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
|
|
* grace period.
|
|
*/
|
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
|
{
|
|
swake_up_all(sq);
|
|
}
|
|
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
|
{
|
|
return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
init_swait_queue_head(&rnp->nocb_gp_wq[0]);
|
|
init_swait_queue_head(&rnp->nocb_gp_wq[1]);
|
|
}
|
|
|
|
/* Is the specified CPU a no-CBs CPU? */
|
|
bool rcu_is_nocb_cpu(int cpu)
|
|
{
|
|
if (cpumask_available(rcu_nocb_mask))
|
|
return cpumask_test_cpu(cpu, rcu_nocb_mask);
|
|
return false;
|
|
}
|
|
|
|
static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
|
|
struct rcu_data *rdp,
|
|
bool force, unsigned long flags)
|
|
__releases(rdp_gp->nocb_gp_lock)
|
|
{
|
|
bool needwake = false;
|
|
|
|
if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
|
|
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("AlreadyAwake"));
|
|
return false;
|
|
}
|
|
|
|
if (rdp_gp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
|
|
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
|
|
del_timer(&rdp_gp->nocb_timer);
|
|
}
|
|
|
|
if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
|
|
WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
|
|
needwake = true;
|
|
}
|
|
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
|
|
if (needwake) {
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
|
|
wake_up_process(rdp_gp->nocb_gp_kthread);
|
|
}
|
|
|
|
return needwake;
|
|
}
|
|
|
|
/*
|
|
* Kick the GP kthread for this NOCB group.
|
|
*/
|
|
static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
|
|
|
|
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
|
|
return __wake_nocb_gp(rdp_gp, rdp, force, flags);
|
|
}
|
|
|
|
/*
|
|
* Arrange to wake the GP kthread for this NOCB group at some future
|
|
* time when it is safe to do so.
|
|
*/
|
|
static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
|
|
const char *reason)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
|
|
|
|
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
|
|
|
|
/*
|
|
* Bypass wakeup overrides previous deferments. In case
|
|
* of callback storm, no need to wake up too early.
|
|
*/
|
|
if (waketype == RCU_NOCB_WAKE_BYPASS) {
|
|
mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
|
|
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
|
|
} else {
|
|
if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE)
|
|
mod_timer(&rdp_gp->nocb_timer, jiffies + 1);
|
|
if (rdp_gp->nocb_defer_wakeup < waketype)
|
|
WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
|
|
}
|
|
|
|
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
|
|
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
|
|
}
|
|
|
|
/*
|
|
* Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
|
|
* However, if there is a callback to be enqueued and if ->nocb_bypass
|
|
* proves to be initially empty, just return false because the no-CB GP
|
|
* kthread may need to be awakened in this case.
|
|
*
|
|
* Note that this function always returns true if rhp is NULL.
|
|
*/
|
|
static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
unsigned long j)
|
|
{
|
|
struct rcu_cblist rcl;
|
|
|
|
WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
|
|
rcu_lockdep_assert_cblist_protected(rdp);
|
|
lockdep_assert_held(&rdp->nocb_bypass_lock);
|
|
if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
|
|
raw_spin_unlock(&rdp->nocb_bypass_lock);
|
|
return false;
|
|
}
|
|
/* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
|
|
if (rhp)
|
|
rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
|
|
rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
|
|
rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
|
|
WRITE_ONCE(rdp->nocb_bypass_first, j);
|
|
rcu_nocb_bypass_unlock(rdp);
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
|
|
* However, if there is a callback to be enqueued and if ->nocb_bypass
|
|
* proves to be initially empty, just return false because the no-CB GP
|
|
* kthread may need to be awakened in this case.
|
|
*
|
|
* Note that this function always returns true if rhp is NULL.
|
|
*/
|
|
static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
unsigned long j)
|
|
{
|
|
if (!rcu_rdp_is_offloaded(rdp))
|
|
return true;
|
|
rcu_lockdep_assert_cblist_protected(rdp);
|
|
rcu_nocb_bypass_lock(rdp);
|
|
return rcu_nocb_do_flush_bypass(rdp, rhp, j);
|
|
}
|
|
|
|
/*
|
|
* If the ->nocb_bypass_lock is immediately available, flush the
|
|
* ->nocb_bypass queue into ->cblist.
|
|
*/
|
|
static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
|
|
{
|
|
rcu_lockdep_assert_cblist_protected(rdp);
|
|
if (!rcu_rdp_is_offloaded(rdp) ||
|
|
!rcu_nocb_bypass_trylock(rdp))
|
|
return;
|
|
WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
|
|
}
|
|
|
|
/*
|
|
* See whether it is appropriate to use the ->nocb_bypass list in order
|
|
* to control contention on ->nocb_lock. A limited number of direct
|
|
* enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
|
|
* is non-empty, further callbacks must be placed into ->nocb_bypass,
|
|
* otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
|
|
* back to direct use of ->cblist. However, ->nocb_bypass should not be
|
|
* used if ->cblist is empty, because otherwise callbacks can be stranded
|
|
* on ->nocb_bypass because we cannot count on the current CPU ever again
|
|
* invoking call_rcu(). The general rule is that if ->nocb_bypass is
|
|
* non-empty, the corresponding no-CBs grace-period kthread must not be
|
|
* in an indefinite sleep state.
|
|
*
|
|
* Finally, it is not permitted to use the bypass during early boot,
|
|
* as doing so would confuse the auto-initialization code. Besides
|
|
* which, there is no point in worrying about lock contention while
|
|
* there is only one CPU in operation.
|
|
*/
|
|
static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool *was_alldone, unsigned long flags)
|
|
{
|
|
unsigned long c;
|
|
unsigned long cur_gp_seq;
|
|
unsigned long j = jiffies;
|
|
long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
|
|
// Pure softirq/rcuc based processing: no bypassing, no
|
|
// locking.
|
|
if (!rcu_rdp_is_offloaded(rdp)) {
|
|
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
|
|
return false;
|
|
}
|
|
|
|
// In the process of (de-)offloading: no bypassing, but
|
|
// locking.
|
|
if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
|
|
rcu_nocb_lock(rdp);
|
|
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
|
|
return false; /* Not offloaded, no bypassing. */
|
|
}
|
|
|
|
// Don't use ->nocb_bypass during early boot.
|
|
if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
|
|
rcu_nocb_lock(rdp);
|
|
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
|
|
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
|
|
return false;
|
|
}
|
|
|
|
// If we have advanced to a new jiffy, reset counts to allow
|
|
// moving back from ->nocb_bypass to ->cblist.
|
|
if (j == rdp->nocb_nobypass_last) {
|
|
c = rdp->nocb_nobypass_count + 1;
|
|
} else {
|
|
WRITE_ONCE(rdp->nocb_nobypass_last, j);
|
|
c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
|
|
if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
|
|
nocb_nobypass_lim_per_jiffy))
|
|
c = 0;
|
|
else if (c > nocb_nobypass_lim_per_jiffy)
|
|
c = nocb_nobypass_lim_per_jiffy;
|
|
}
|
|
WRITE_ONCE(rdp->nocb_nobypass_count, c);
|
|
|
|
// If there hasn't yet been all that many ->cblist enqueues
|
|
// this jiffy, tell the caller to enqueue onto ->cblist. But flush
|
|
// ->nocb_bypass first.
|
|
if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
|
|
rcu_nocb_lock(rdp);
|
|
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
|
|
if (*was_alldone)
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstQ"));
|
|
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
|
|
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
|
|
return false; // Caller must enqueue the callback.
|
|
}
|
|
|
|
// If ->nocb_bypass has been used too long or is too full,
|
|
// flush ->nocb_bypass to ->cblist.
|
|
if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
|
|
ncbs >= qhimark) {
|
|
rcu_nocb_lock(rdp);
|
|
if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
|
|
*was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
|
|
if (*was_alldone)
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstQ"));
|
|
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
|
|
return false; // Caller must enqueue the callback.
|
|
}
|
|
if (j != rdp->nocb_gp_adv_time &&
|
|
rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
|
|
rcu_advance_cbs_nowake(rdp->mynode, rdp);
|
|
rdp->nocb_gp_adv_time = j;
|
|
}
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
return true; // Callback already enqueued.
|
|
}
|
|
|
|
// We need to use the bypass.
|
|
rcu_nocb_wait_contended(rdp);
|
|
rcu_nocb_bypass_lock(rdp);
|
|
ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
|
|
rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
|
|
rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
|
|
if (!ncbs) {
|
|
WRITE_ONCE(rdp->nocb_bypass_first, j);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
|
|
}
|
|
rcu_nocb_bypass_unlock(rdp);
|
|
smp_mb(); /* Order enqueue before wake. */
|
|
if (ncbs) {
|
|
local_irq_restore(flags);
|
|
} else {
|
|
// No-CBs GP kthread might be indefinitely asleep, if so, wake.
|
|
rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
|
|
if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstBQwake"));
|
|
__call_rcu_nocb_wake(rdp, true, flags);
|
|
} else {
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("FirstBQnoWake"));
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
}
|
|
}
|
|
return true; // Callback already enqueued.
|
|
}
|
|
|
|
/*
|
|
* Awaken the no-CBs grace-period kthead if needed, either due to it
|
|
* legitimately being asleep or due to overload conditions.
|
|
*
|
|
* If warranted, also wake up the kthread servicing this CPUs queues.
|
|
*/
|
|
static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
|
|
unsigned long flags)
|
|
__releases(rdp->nocb_lock)
|
|
{
|
|
unsigned long cur_gp_seq;
|
|
unsigned long j;
|
|
long len;
|
|
struct task_struct *t;
|
|
|
|
// If we are being polled or there is no kthread, just leave.
|
|
t = READ_ONCE(rdp->nocb_gp_kthread);
|
|
if (rcu_nocb_poll || !t) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("WakeNotPoll"));
|
|
return;
|
|
}
|
|
// Need to actually to a wakeup.
|
|
len = rcu_segcblist_n_cbs(&rdp->cblist);
|
|
if (was_alldone) {
|
|
rdp->qlen_last_fqs_check = len;
|
|
if (!irqs_disabled_flags(flags)) {
|
|
/* ... if queue was empty ... */
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
wake_nocb_gp(rdp, false);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("WakeEmpty"));
|
|
} else {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
|
|
TPS("WakeEmptyIsDeferred"));
|
|
}
|
|
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
|
|
/* ... or if many callbacks queued. */
|
|
rdp->qlen_last_fqs_check = len;
|
|
j = jiffies;
|
|
if (j != rdp->nocb_gp_adv_time &&
|
|
rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
|
|
rcu_advance_cbs_nowake(rdp->mynode, rdp);
|
|
rdp->nocb_gp_adv_time = j;
|
|
}
|
|
smp_mb(); /* Enqueue before timer_pending(). */
|
|
if ((rdp->nocb_cb_sleep ||
|
|
!rcu_segcblist_ready_cbs(&rdp->cblist)) &&
|
|
!timer_pending(&rdp->nocb_timer)) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
|
|
TPS("WakeOvfIsDeferred"));
|
|
} else {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
|
|
}
|
|
} else {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
|
|
}
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Check if we ignore this rdp.
|
|
*
|
|
* We check that without holding the nocb lock but
|
|
* we make sure not to miss a freshly offloaded rdp
|
|
* with the current ordering:
|
|
*
|
|
* rdp_offload_toggle() nocb_gp_enabled_cb()
|
|
* ------------------------- ----------------------------
|
|
* WRITE flags LOCK nocb_gp_lock
|
|
* LOCK nocb_gp_lock READ/WRITE nocb_gp_sleep
|
|
* READ/WRITE nocb_gp_sleep UNLOCK nocb_gp_lock
|
|
* UNLOCK nocb_gp_lock READ flags
|
|
*/
|
|
static inline bool nocb_gp_enabled_cb(struct rcu_data *rdp)
|
|
{
|
|
u8 flags = SEGCBLIST_OFFLOADED | SEGCBLIST_KTHREAD_GP;
|
|
|
|
return rcu_segcblist_test_flags(&rdp->cblist, flags);
|
|
}
|
|
|
|
static inline bool nocb_gp_update_state_deoffloading(struct rcu_data *rdp,
|
|
bool *needwake_state)
|
|
{
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) {
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)) {
|
|
rcu_segcblist_set_flags(cblist, SEGCBLIST_KTHREAD_GP);
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB))
|
|
*needwake_state = true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* De-offloading. Clear our flag and notify the de-offload worker.
|
|
* We will ignore this rdp until it ever gets re-offloaded.
|
|
*/
|
|
WARN_ON_ONCE(!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP));
|
|
rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_GP);
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB))
|
|
*needwake_state = true;
|
|
return true;
|
|
}
|
|
|
|
|
|
/*
|
|
* No-CBs GP kthreads come here to wait for additional callbacks to show up
|
|
* or for grace periods to end.
|
|
*/
|
|
static void nocb_gp_wait(struct rcu_data *my_rdp)
|
|
{
|
|
bool bypass = false;
|
|
long bypass_ncbs;
|
|
int __maybe_unused cpu = my_rdp->cpu;
|
|
unsigned long cur_gp_seq;
|
|
unsigned long flags;
|
|
bool gotcbs = false;
|
|
unsigned long j = jiffies;
|
|
bool needwait_gp = false; // This prevents actual uninitialized use.
|
|
bool needwake;
|
|
bool needwake_gp;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp;
|
|
unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
|
|
bool wasempty = false;
|
|
|
|
/*
|
|
* Each pass through the following loop checks for CBs and for the
|
|
* nearest grace period (if any) to wait for next. The CB kthreads
|
|
* and the global grace-period kthread are awakened if needed.
|
|
*/
|
|
WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
|
|
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
|
|
bool needwake_state = false;
|
|
|
|
if (!nocb_gp_enabled_cb(rdp))
|
|
continue;
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
if (nocb_gp_update_state_deoffloading(rdp, &needwake_state)) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
continue;
|
|
}
|
|
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
|
|
if (bypass_ncbs &&
|
|
(time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
|
|
bypass_ncbs > 2 * qhimark)) {
|
|
// Bypass full or old, so flush it.
|
|
(void)rcu_nocb_try_flush_bypass(rdp, j);
|
|
bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
|
|
} else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
continue; /* No callbacks here, try next. */
|
|
}
|
|
if (bypass_ncbs) {
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("Bypass"));
|
|
bypass = true;
|
|
}
|
|
rnp = rdp->mynode;
|
|
|
|
// Advance callbacks if helpful and low contention.
|
|
needwake_gp = false;
|
|
if (!rcu_segcblist_restempty(&rdp->cblist,
|
|
RCU_NEXT_READY_TAIL) ||
|
|
(rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
|
|
raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
|
|
needwake_gp = rcu_advance_cbs(rnp, rdp);
|
|
wasempty = rcu_segcblist_restempty(&rdp->cblist,
|
|
RCU_NEXT_READY_TAIL);
|
|
raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
|
|
}
|
|
// Need to wait on some grace period?
|
|
WARN_ON_ONCE(wasempty &&
|
|
!rcu_segcblist_restempty(&rdp->cblist,
|
|
RCU_NEXT_READY_TAIL));
|
|
if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
|
|
if (!needwait_gp ||
|
|
ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
|
|
wait_gp_seq = cur_gp_seq;
|
|
needwait_gp = true;
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
|
|
TPS("NeedWaitGP"));
|
|
}
|
|
if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
|
|
needwake = rdp->nocb_cb_sleep;
|
|
WRITE_ONCE(rdp->nocb_cb_sleep, false);
|
|
smp_mb(); /* CB invocation -after- GP end. */
|
|
} else {
|
|
needwake = false;
|
|
}
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake) {
|
|
swake_up_one(&rdp->nocb_cb_wq);
|
|
gotcbs = true;
|
|
}
|
|
if (needwake_gp)
|
|
rcu_gp_kthread_wake();
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
}
|
|
|
|
my_rdp->nocb_gp_bypass = bypass;
|
|
my_rdp->nocb_gp_gp = needwait_gp;
|
|
my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
|
|
|
|
if (bypass && !rcu_nocb_poll) {
|
|
// At least one child with non-empty ->nocb_bypass, so set
|
|
// timer in order to avoid stranding its callbacks.
|
|
wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
|
|
TPS("WakeBypassIsDeferred"));
|
|
}
|
|
if (rcu_nocb_poll) {
|
|
/* Polling, so trace if first poll in the series. */
|
|
if (gotcbs)
|
|
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
|
|
schedule_timeout_idle(1);
|
|
} else if (!needwait_gp) {
|
|
/* Wait for callbacks to appear. */
|
|
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
|
|
swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
|
|
!READ_ONCE(my_rdp->nocb_gp_sleep));
|
|
trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
|
|
} else {
|
|
rnp = my_rdp->mynode;
|
|
trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
|
|
swait_event_interruptible_exclusive(
|
|
rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
|
|
rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
|
|
!READ_ONCE(my_rdp->nocb_gp_sleep));
|
|
trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
|
|
}
|
|
if (!rcu_nocb_poll) {
|
|
raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
|
|
if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
|
|
WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
|
|
del_timer(&my_rdp->nocb_timer);
|
|
}
|
|
WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
|
|
raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
|
|
}
|
|
my_rdp->nocb_gp_seq = -1;
|
|
WARN_ON(signal_pending(current));
|
|
}
|
|
|
|
/*
|
|
* No-CBs grace-period-wait kthread. There is one of these per group
|
|
* of CPUs, but only once at least one CPU in that group has come online
|
|
* at least once since boot. This kthread checks for newly posted
|
|
* callbacks from any of the CPUs it is responsible for, waits for a
|
|
* grace period, then awakens all of the rcu_nocb_cb_kthread() instances
|
|
* that then have callback-invocation work to do.
|
|
*/
|
|
static int rcu_nocb_gp_kthread(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
|
|
for (;;) {
|
|
WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
|
|
nocb_gp_wait(rdp);
|
|
cond_resched_tasks_rcu_qs();
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
static inline bool nocb_cb_can_run(struct rcu_data *rdp)
|
|
{
|
|
u8 flags = SEGCBLIST_OFFLOADED | SEGCBLIST_KTHREAD_CB;
|
|
return rcu_segcblist_test_flags(&rdp->cblist, flags);
|
|
}
|
|
|
|
static inline bool nocb_cb_wait_cond(struct rcu_data *rdp)
|
|
{
|
|
return nocb_cb_can_run(rdp) && !READ_ONCE(rdp->nocb_cb_sleep);
|
|
}
|
|
|
|
/*
|
|
* Invoke any ready callbacks from the corresponding no-CBs CPU,
|
|
* then, if there are no more, wait for more to appear.
|
|
*/
|
|
static void nocb_cb_wait(struct rcu_data *rdp)
|
|
{
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
unsigned long cur_gp_seq;
|
|
unsigned long flags;
|
|
bool needwake_state = false;
|
|
bool needwake_gp = false;
|
|
bool can_sleep = true;
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
local_irq_save(flags);
|
|
rcu_momentary_dyntick_idle();
|
|
local_irq_restore(flags);
|
|
/*
|
|
* Disable BH to provide the expected environment. Also, when
|
|
* transitioning to/from NOCB mode, a self-requeuing callback might
|
|
* be invoked from softirq. A short grace period could cause both
|
|
* instances of this callback would execute concurrently.
|
|
*/
|
|
local_bh_disable();
|
|
rcu_do_batch(rdp);
|
|
local_bh_enable();
|
|
lockdep_assert_irqs_enabled();
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
if (rcu_segcblist_nextgp(cblist, &cur_gp_seq) &&
|
|
rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
|
|
raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
|
|
needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
|
|
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
|
}
|
|
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) {
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)) {
|
|
rcu_segcblist_set_flags(cblist, SEGCBLIST_KTHREAD_CB);
|
|
if (rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP))
|
|
needwake_state = true;
|
|
}
|
|
if (rcu_segcblist_ready_cbs(cblist))
|
|
can_sleep = false;
|
|
} else {
|
|
/*
|
|
* De-offloading. Clear our flag and notify the de-offload worker.
|
|
* We won't touch the callbacks and keep sleeping until we ever
|
|
* get re-offloaded.
|
|
*/
|
|
WARN_ON_ONCE(!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB));
|
|
rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_CB);
|
|
if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP))
|
|
needwake_state = true;
|
|
}
|
|
|
|
WRITE_ONCE(rdp->nocb_cb_sleep, can_sleep);
|
|
|
|
if (rdp->nocb_cb_sleep)
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
|
|
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
if (needwake_gp)
|
|
rcu_gp_kthread_wake();
|
|
|
|
if (needwake_state)
|
|
swake_up_one(&rdp->nocb_state_wq);
|
|
|
|
do {
|
|
swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
|
|
nocb_cb_wait_cond(rdp));
|
|
|
|
// VVV Ensure CB invocation follows _sleep test.
|
|
if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^
|
|
WARN_ON(signal_pending(current));
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
|
|
}
|
|
} while (!nocb_cb_can_run(rdp));
|
|
}
|
|
|
|
/*
|
|
* Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
|
|
* nocb_cb_wait() to do the dirty work.
|
|
*/
|
|
static int rcu_nocb_cb_kthread(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
|
|
// Each pass through this loop does one callback batch, and,
|
|
// if there are no more ready callbacks, waits for them.
|
|
for (;;) {
|
|
nocb_cb_wait(rdp);
|
|
cond_resched_tasks_rcu_qs();
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
|
|
{
|
|
return READ_ONCE(rdp->nocb_defer_wakeup) >= level;
|
|
}
|
|
|
|
/* Do a deferred wakeup of rcu_nocb_kthread(). */
|
|
static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp_gp,
|
|
struct rcu_data *rdp, int level,
|
|
unsigned long flags)
|
|
__releases(rdp_gp->nocb_gp_lock)
|
|
{
|
|
int ndw;
|
|
int ret;
|
|
|
|
if (!rcu_nocb_need_deferred_wakeup(rdp_gp, level)) {
|
|
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
|
|
return false;
|
|
}
|
|
|
|
ndw = rdp_gp->nocb_defer_wakeup;
|
|
ret = __wake_nocb_gp(rdp_gp, rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
|
|
|
|
return ret;
|
|
}
|
|
|
|
/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
|
|
static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
|
|
|
|
WARN_ON_ONCE(rdp->nocb_gp_rdp != rdp);
|
|
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
|
|
|
|
raw_spin_lock_irqsave(&rdp->nocb_gp_lock, flags);
|
|
smp_mb__after_spinlock(); /* Timer expire before wakeup. */
|
|
do_nocb_deferred_wakeup_common(rdp, rdp, RCU_NOCB_WAKE_BYPASS, flags);
|
|
}
|
|
|
|
/*
|
|
* Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
|
|
* This means we do an inexact common-case check. Note that if
|
|
* we miss, ->nocb_timer will eventually clean things up.
|
|
*/
|
|
static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
|
|
|
|
if (!rdp_gp || !rcu_nocb_need_deferred_wakeup(rdp_gp, RCU_NOCB_WAKE))
|
|
return false;
|
|
|
|
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
|
|
return do_nocb_deferred_wakeup_common(rdp_gp, rdp, RCU_NOCB_WAKE, flags);
|
|
}
|
|
|
|
void rcu_nocb_flush_deferred_wakeup(void)
|
|
{
|
|
do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup);
|
|
|
|
static int rdp_offload_toggle(struct rcu_data *rdp,
|
|
bool offload, unsigned long flags)
|
|
__releases(rdp->nocb_lock)
|
|
{
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
|
|
bool wake_gp = false;
|
|
|
|
rcu_segcblist_offload(cblist, offload);
|
|
|
|
if (rdp->nocb_cb_sleep)
|
|
rdp->nocb_cb_sleep = false;
|
|
rcu_nocb_unlock_irqrestore(rdp, flags);
|
|
|
|
/*
|
|
* Ignore former value of nocb_cb_sleep and force wake up as it could
|
|
* have been spuriously set to false already.
|
|
*/
|
|
swake_up_one(&rdp->nocb_cb_wq);
|
|
|
|
raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
|
|
if (rdp_gp->nocb_gp_sleep) {
|
|
rdp_gp->nocb_gp_sleep = false;
|
|
wake_gp = true;
|
|
}
|
|
raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
|
|
|
|
if (wake_gp)
|
|
wake_up_process(rdp_gp->nocb_gp_kthread);
|
|
|
|
return 0;
|
|
}
|
|
|
|
static long rcu_nocb_rdp_deoffload(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
unsigned long flags;
|
|
int ret;
|
|
|
|
WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id());
|
|
|
|
pr_info("De-offloading %d\n", rdp->cpu);
|
|
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
/*
|
|
* Flush once and for all now. This suffices because we are
|
|
* running on the target CPU holding ->nocb_lock (thus having
|
|
* interrupts disabled), and because rdp_offload_toggle()
|
|
* invokes rcu_segcblist_offload(), which clears SEGCBLIST_OFFLOADED.
|
|
* Thus future calls to rcu_segcblist_completely_offloaded() will
|
|
* return false, which means that future calls to rcu_nocb_try_bypass()
|
|
* will refuse to put anything into the bypass.
|
|
*/
|
|
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
|
|
ret = rdp_offload_toggle(rdp, false, flags);
|
|
swait_event_exclusive(rdp->nocb_state_wq,
|
|
!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB |
|
|
SEGCBLIST_KTHREAD_GP));
|
|
/*
|
|
* Lock one last time to acquire latest callback updates from kthreads
|
|
* so we can later handle callbacks locally without locking.
|
|
*/
|
|
rcu_nocb_lock_irqsave(rdp, flags);
|
|
/*
|
|
* Theoretically we could set SEGCBLIST_SOFTIRQ_ONLY after the nocb
|
|
* lock is released but how about being paranoid for once?
|
|
*/
|
|
rcu_segcblist_set_flags(cblist, SEGCBLIST_SOFTIRQ_ONLY);
|
|
/*
|
|
* With SEGCBLIST_SOFTIRQ_ONLY, we can't use
|
|
* rcu_nocb_unlock_irqrestore() anymore.
|
|
*/
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
|
|
/* Sanity check */
|
|
WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
|
|
|
|
|
|
return ret;
|
|
}
|
|
|
|
int rcu_nocb_cpu_deoffload(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
int ret = 0;
|
|
|
|
mutex_lock(&rcu_state.barrier_mutex);
|
|
cpus_read_lock();
|
|
if (rcu_rdp_is_offloaded(rdp)) {
|
|
if (cpu_online(cpu)) {
|
|
ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp);
|
|
if (!ret)
|
|
cpumask_clear_cpu(cpu, rcu_nocb_mask);
|
|
} else {
|
|
pr_info("NOCB: Can't CB-deoffload an offline CPU\n");
|
|
ret = -EINVAL;
|
|
}
|
|
}
|
|
cpus_read_unlock();
|
|
mutex_unlock(&rcu_state.barrier_mutex);
|
|
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload);
|
|
|
|
static long rcu_nocb_rdp_offload(void *arg)
|
|
{
|
|
struct rcu_data *rdp = arg;
|
|
struct rcu_segcblist *cblist = &rdp->cblist;
|
|
unsigned long flags;
|
|
int ret;
|
|
|
|
WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id());
|
|
/*
|
|
* For now we only support re-offload, ie: the rdp must have been
|
|
* offloaded on boot first.
|
|
*/
|
|
if (!rdp->nocb_gp_rdp)
|
|
return -EINVAL;
|
|
|
|
pr_info("Offloading %d\n", rdp->cpu);
|
|
/*
|
|
* Can't use rcu_nocb_lock_irqsave() while we are in
|
|
* SEGCBLIST_SOFTIRQ_ONLY mode.
|
|
*/
|
|
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
|
|
|
|
/*
|
|
* We didn't take the nocb lock while working on the
|
|
* rdp->cblist in SEGCBLIST_SOFTIRQ_ONLY mode.
|
|
* Every modifications that have been done previously on
|
|
* rdp->cblist must be visible remotely by the nocb kthreads
|
|
* upon wake up after reading the cblist flags.
|
|
*
|
|
* The layout against nocb_lock enforces that ordering:
|
|
*
|
|
* __rcu_nocb_rdp_offload() nocb_cb_wait()/nocb_gp_wait()
|
|
* ------------------------- ----------------------------
|
|
* WRITE callbacks rcu_nocb_lock()
|
|
* rcu_nocb_lock() READ flags
|
|
* WRITE flags READ callbacks
|
|
* rcu_nocb_unlock() rcu_nocb_unlock()
|
|
*/
|
|
ret = rdp_offload_toggle(rdp, true, flags);
|
|
swait_event_exclusive(rdp->nocb_state_wq,
|
|
rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) &&
|
|
rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP));
|
|
|
|
return ret;
|
|
}
|
|
|
|
int rcu_nocb_cpu_offload(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
int ret = 0;
|
|
|
|
mutex_lock(&rcu_state.barrier_mutex);
|
|
cpus_read_lock();
|
|
if (!rcu_rdp_is_offloaded(rdp)) {
|
|
if (cpu_online(cpu)) {
|
|
ret = work_on_cpu(cpu, rcu_nocb_rdp_offload, rdp);
|
|
if (!ret)
|
|
cpumask_set_cpu(cpu, rcu_nocb_mask);
|
|
} else {
|
|
pr_info("NOCB: Can't CB-offload an offline CPU\n");
|
|
ret = -EINVAL;
|
|
}
|
|
}
|
|
cpus_read_unlock();
|
|
mutex_unlock(&rcu_state.barrier_mutex);
|
|
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
|
|
|
|
void __init rcu_init_nohz(void)
|
|
{
|
|
int cpu;
|
|
bool need_rcu_nocb_mask = false;
|
|
struct rcu_data *rdp;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
|
|
need_rcu_nocb_mask = true;
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
|
|
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
|
|
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
|
|
return;
|
|
}
|
|
}
|
|
if (!cpumask_available(rcu_nocb_mask))
|
|
return;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running)
|
|
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
|
|
pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
|
|
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
|
|
rcu_nocb_mask);
|
|
}
|
|
if (cpumask_empty(rcu_nocb_mask))
|
|
pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
|
|
else
|
|
pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
|
|
cpumask_pr_args(rcu_nocb_mask));
|
|
if (rcu_nocb_poll)
|
|
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
|
|
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
if (rcu_segcblist_empty(&rdp->cblist))
|
|
rcu_segcblist_init(&rdp->cblist);
|
|
rcu_segcblist_offload(&rdp->cblist, true);
|
|
rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB);
|
|
rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_GP);
|
|
}
|
|
rcu_organize_nocb_kthreads();
|
|
}
|
|
|
|
/* Initialize per-rcu_data variables for no-CBs CPUs. */
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
init_swait_queue_head(&rdp->nocb_cb_wq);
|
|
init_swait_queue_head(&rdp->nocb_gp_wq);
|
|
init_swait_queue_head(&rdp->nocb_state_wq);
|
|
raw_spin_lock_init(&rdp->nocb_lock);
|
|
raw_spin_lock_init(&rdp->nocb_bypass_lock);
|
|
raw_spin_lock_init(&rdp->nocb_gp_lock);
|
|
timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
|
|
rcu_cblist_init(&rdp->nocb_bypass);
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
|
|
* for this CPU's group has not yet been created, spawn it as well.
|
|
*/
|
|
static void rcu_spawn_one_nocb_kthread(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
struct rcu_data *rdp_gp;
|
|
struct task_struct *t;
|
|
|
|
/*
|
|
* If this isn't a no-CBs CPU or if it already has an rcuo kthread,
|
|
* then nothing to do.
|
|
*/
|
|
if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
|
|
return;
|
|
|
|
/* If we didn't spawn the GP kthread first, reorganize! */
|
|
rdp_gp = rdp->nocb_gp_rdp;
|
|
if (!rdp_gp->nocb_gp_kthread) {
|
|
t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
|
|
"rcuog/%d", rdp_gp->cpu);
|
|
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
|
|
return;
|
|
WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
|
|
}
|
|
|
|
/* Spawn the kthread for this CPU. */
|
|
t = kthread_run(rcu_nocb_cb_kthread, rdp,
|
|
"rcuo%c/%d", rcu_state.abbr, cpu);
|
|
if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
|
|
return;
|
|
WRITE_ONCE(rdp->nocb_cb_kthread, t);
|
|
WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo kthread, spawn it.
|
|
*/
|
|
static void rcu_spawn_cpu_nocb_kthread(int cpu)
|
|
{
|
|
if (rcu_scheduler_fully_active)
|
|
rcu_spawn_one_nocb_kthread(cpu);
|
|
}
|
|
|
|
/*
|
|
* Once the scheduler is running, spawn rcuo kthreads for all online
|
|
* no-CBs CPUs. This assumes that the early_initcall()s happen before
|
|
* non-boot CPUs come online -- if this changes, we will need to add
|
|
* some mutual exclusion.
|
|
*/
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
int cpu;
|
|
|
|
for_each_online_cpu(cpu)
|
|
rcu_spawn_cpu_nocb_kthread(cpu);
|
|
}
|
|
|
|
/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
|
|
static int rcu_nocb_gp_stride = -1;
|
|
module_param(rcu_nocb_gp_stride, int, 0444);
|
|
|
|
/*
|
|
* Initialize GP-CB relationships for all no-CBs CPU.
|
|
*/
|
|
static void __init rcu_organize_nocb_kthreads(void)
|
|
{
|
|
int cpu;
|
|
bool firsttime = true;
|
|
bool gotnocbs = false;
|
|
bool gotnocbscbs = true;
|
|
int ls = rcu_nocb_gp_stride;
|
|
int nl = 0; /* Next GP kthread. */
|
|
struct rcu_data *rdp;
|
|
struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
|
|
struct rcu_data *rdp_prev = NULL;
|
|
|
|
if (!cpumask_available(rcu_nocb_mask))
|
|
return;
|
|
if (ls == -1) {
|
|
ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
|
|
rcu_nocb_gp_stride = ls;
|
|
}
|
|
|
|
/*
|
|
* Each pass through this loop sets up one rcu_data structure.
|
|
* Should the corresponding CPU come online in the future, then
|
|
* we will spawn the needed set of rcu_nocb_kthread() kthreads.
|
|
*/
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
if (rdp->cpu >= nl) {
|
|
/* New GP kthread, set up for CBs & next GP. */
|
|
gotnocbs = true;
|
|
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
|
|
rdp->nocb_gp_rdp = rdp;
|
|
rdp_gp = rdp;
|
|
if (dump_tree) {
|
|
if (!firsttime)
|
|
pr_cont("%s\n", gotnocbscbs
|
|
? "" : " (self only)");
|
|
gotnocbscbs = false;
|
|
firsttime = false;
|
|
pr_alert("%s: No-CB GP kthread CPU %d:",
|
|
__func__, cpu);
|
|
}
|
|
} else {
|
|
/* Another CB kthread, link to previous GP kthread. */
|
|
gotnocbscbs = true;
|
|
rdp->nocb_gp_rdp = rdp_gp;
|
|
rdp_prev->nocb_next_cb_rdp = rdp;
|
|
if (dump_tree)
|
|
pr_cont(" %d", cpu);
|
|
}
|
|
rdp_prev = rdp;
|
|
}
|
|
if (gotnocbs && dump_tree)
|
|
pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
|
|
}
|
|
|
|
/*
|
|
* Bind the current task to the offloaded CPUs. If there are no offloaded
|
|
* CPUs, leave the task unbound. Splat if the bind attempt fails.
|
|
*/
|
|
void rcu_bind_current_to_nocb(void)
|
|
{
|
|
if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
|
|
WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
|
|
|
|
// The ->on_cpu field is available only in CONFIG_SMP=y, so...
|
|
#ifdef CONFIG_SMP
|
|
static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
|
|
{
|
|
return tsp && tsp->state == TASK_RUNNING && !tsp->on_cpu ? "!" : "";
|
|
}
|
|
#else // #ifdef CONFIG_SMP
|
|
static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
|
|
{
|
|
return "";
|
|
}
|
|
#endif // #else #ifdef CONFIG_SMP
|
|
|
|
/*
|
|
* Dump out nocb grace-period kthread state for the specified rcu_data
|
|
* structure.
|
|
*/
|
|
static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
|
|
{
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
pr_info("nocb GP %d %c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu %c CPU %d%s\n",
|
|
rdp->cpu,
|
|
"kK"[!!rdp->nocb_gp_kthread],
|
|
"lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
|
|
"dD"[!!rdp->nocb_defer_wakeup],
|
|
"tT"[timer_pending(&rdp->nocb_timer)],
|
|
"sS"[!!rdp->nocb_gp_sleep],
|
|
".W"[swait_active(&rdp->nocb_gp_wq)],
|
|
".W"[swait_active(&rnp->nocb_gp_wq[0])],
|
|
".W"[swait_active(&rnp->nocb_gp_wq[1])],
|
|
".B"[!!rdp->nocb_gp_bypass],
|
|
".G"[!!rdp->nocb_gp_gp],
|
|
(long)rdp->nocb_gp_seq,
|
|
rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops),
|
|
rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.',
|
|
rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
|
|
show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
|
|
}
|
|
|
|
/* Dump out nocb kthread state for the specified rcu_data structure. */
|
|
static void show_rcu_nocb_state(struct rcu_data *rdp)
|
|
{
|
|
char bufw[20];
|
|
char bufr[20];
|
|
struct rcu_segcblist *rsclp = &rdp->cblist;
|
|
bool waslocked;
|
|
bool wassleep;
|
|
|
|
if (rdp->nocb_gp_rdp == rdp)
|
|
show_rcu_nocb_gp_state(rdp);
|
|
|
|
sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]);
|
|
sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
|
|
pr_info(" CB %d^%d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n",
|
|
rdp->cpu, rdp->nocb_gp_rdp->cpu,
|
|
rdp->nocb_next_cb_rdp ? rdp->nocb_next_cb_rdp->cpu : -1,
|
|
"kK"[!!rdp->nocb_cb_kthread],
|
|
"bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
|
|
"cC"[!!atomic_read(&rdp->nocb_lock_contended)],
|
|
"lL"[raw_spin_is_locked(&rdp->nocb_lock)],
|
|
"sS"[!!rdp->nocb_cb_sleep],
|
|
".W"[swait_active(&rdp->nocb_cb_wq)],
|
|
jiffies - rdp->nocb_bypass_first,
|
|
jiffies - rdp->nocb_nobypass_last,
|
|
rdp->nocb_nobypass_count,
|
|
".D"[rcu_segcblist_ready_cbs(rsclp)],
|
|
".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)],
|
|
rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw,
|
|
".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)],
|
|
rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr,
|
|
".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)],
|
|
".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
|
|
rcu_segcblist_n_cbs(&rdp->cblist),
|
|
rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
|
|
rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
|
|
show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
|
|
|
|
/* It is OK for GP kthreads to have GP state. */
|
|
if (rdp->nocb_gp_rdp == rdp)
|
|
return;
|
|
|
|
waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
|
|
wassleep = swait_active(&rdp->nocb_gp_wq);
|
|
if (!rdp->nocb_gp_sleep && !waslocked && !wassleep)
|
|
return; /* Nothing untowards. */
|
|
|
|
pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c %c\n",
|
|
"lL"[waslocked],
|
|
"dD"[!!rdp->nocb_defer_wakeup],
|
|
"sS"[!!rdp->nocb_gp_sleep],
|
|
".W"[wassleep]);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
/* No ->nocb_lock to acquire. */
|
|
static void rcu_nocb_lock(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
/* No ->nocb_lock to release. */
|
|
static void rcu_nocb_unlock(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
/* No ->nocb_lock to release. */
|
|
static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
|
|
unsigned long flags)
|
|
{
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/* Lockdep check that ->cblist may be safely accessed. */
|
|
static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
}
|
|
|
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
|
{
|
|
}
|
|
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
|
{
|
|
return NULL;
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
unsigned long j)
|
|
{
|
|
return true;
|
|
}
|
|
|
|
static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool *was_alldone, unsigned long flags)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
|
|
unsigned long flags)
|
|
{
|
|
WARN_ON_ONCE(1); /* Should be dead code! */
|
|
}
|
|
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_spawn_cpu_nocb_kthread(int cpu)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
}
|
|
|
|
static void show_rcu_nocb_state(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
/*
|
|
* Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
|
|
* grace-period kthread will do force_quiescent_state() processing?
|
|
* The idea is to avoid waking up RCU core processing on such a
|
|
* CPU unless the grace period has extended for too long.
|
|
*
|
|
* This code relies on the fact that all NO_HZ_FULL CPUs are also
|
|
* CONFIG_RCU_NOCB_CPU CPUs.
|
|
*/
|
|
static bool rcu_nohz_full_cpu(void)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (tick_nohz_full_cpu(smp_processor_id()) &&
|
|
(!rcu_gp_in_progress() ||
|
|
time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
|
|
return true;
|
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Bind the RCU grace-period kthreads to the housekeeping CPU.
|
|
*/
|
|
static void rcu_bind_gp_kthread(void)
|
|
{
|
|
if (!tick_nohz_full_enabled())
|
|
return;
|
|
housekeeping_affine(current, HK_FLAG_RCU);
|
|
}
|
|
|
|
/* Record the current task on dyntick-idle entry. */
|
|
static void noinstr rcu_dynticks_task_enter(void)
|
|
{
|
|
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
|
|
WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
|
|
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
|
|
}
|
|
|
|
/* Record no current task on dyntick-idle exit. */
|
|
static void noinstr rcu_dynticks_task_exit(void)
|
|
{
|
|
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
|
|
WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
|
|
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
|
|
}
|
|
|
|
/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */
|
|
static void rcu_dynticks_task_trace_enter(void)
|
|
{
|
|
#ifdef CONFIG_TASKS_RCU_TRACE
|
|
if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
|
|
current->trc_reader_special.b.need_mb = true;
|
|
#endif /* #ifdef CONFIG_TASKS_RCU_TRACE */
|
|
}
|
|
|
|
/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */
|
|
static void rcu_dynticks_task_trace_exit(void)
|
|
{
|
|
#ifdef CONFIG_TASKS_RCU_TRACE
|
|
if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
|
|
current->trc_reader_special.b.need_mb = false;
|
|
#endif /* #ifdef CONFIG_TASKS_RCU_TRACE */
|
|
}
|