From dfcb27540213e8061ecffacd4bd8ed54a310a7b0 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 19 May 2021 02:09:28 +0200 Subject: [PATCH] rcu/nocb: Start moving nocb code to its own plugin file The kernel/rcu/tree_plugin.h file contains not only the plugins for preemptible RCU, but also many other features including rcu_nocbs callback offloading. This offloading has become large and complex, so it is time to put it in its own file. This commit starts that process. Suggested-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker [ paulmck: Rename to tree_nocb.h, add Frederic as author. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 1 + kernel/rcu/tree_nocb.h | 1496 ++++++++++++++++++++++++++++++++++++++ kernel/rcu/tree_plugin.h | 1487 ------------------------------------- 3 files changed, 1497 insertions(+), 1487 deletions(-) create mode 100644 kernel/rcu/tree_nocb.h diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 51f24ecd94b2..b6eb480402e0 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4784,4 +4784,5 @@ void __init rcu_init(void) #include "tree_stall.h" #include "tree_exp.h" +#include "tree_nocb.h" #include "tree_plugin.h" diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h new file mode 100644 index 000000000000..8fdf44f8523f --- /dev/null +++ b/kernel/rcu/tree_nocb.h @@ -0,0 +1,1496 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Read-Copy Update mechanism for mutual exclusion (tree-based version) + * Internal non-public definitions that provide either classic + * or preemptible semantics. + * + * Copyright Red Hat, 2009 + * Copyright IBM Corporation, 2009 + * Copyright SUSE, 2021 + * + * Author: Ingo Molnar + * Paul E. McKenney + * Frederic Weisbecker + */ + +#ifdef CONFIG_RCU_NOCB_CPU +static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ +static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ +static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) +{ + return lockdep_is_held(&rdp->nocb_lock); +} + +static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) +{ + /* Race on early boot between thread creation and assignment */ + if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread) + return true; + + if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread) + if (in_task()) + return true; + return false; +} + +/* + * 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 (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 kthread 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 && task_is_running(tsp) && !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 untoward. */ + + 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 */ + +static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) +{ + return 0; +} + +static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) +{ + return false; +} + +/* 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 */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index de1dc3bb7f70..aec5075c60b3 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -13,39 +13,6 @@ #include "../locking/rtmutex_common.h" -#ifdef CONFIG_RCU_NOCB_CPU -static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ -static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ -static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) -{ - return lockdep_is_held(&rdp->nocb_lock); -} - -static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) -{ - /* Race on early boot between thread creation and assignment */ - if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread) - return true; - - if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread) - if (in_task()) - return true; - return false; -} - -#else -static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) -{ - return 0; -} - -static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) -{ - return false; -} - -#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ - static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) { /* @@ -1479,1460 +1446,6 @@ static void rcu_cleanup_after_idle(void) #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 (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 kthread 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 && task_is_running(tsp) && !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 untoward. */ - - 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?