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433cdddcd9
This commit adds trace_rcu_prep_idle(), which is invoked from rcu_prepare_for_idle() and rcu_wake_cpu() to trace attempts on the part of RCU to force CPUs into dyntick-idle mode. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2139 lines
62 KiB
C
2139 lines
62 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright Red Hat, 2009
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* Copyright IBM Corporation, 2009
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#include <linux/delay.h>
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#include <linux/stop_machine.h>
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#define RCU_KTHREAD_PRIO 1
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#ifdef CONFIG_RCU_BOOST
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#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
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#else
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#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
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#endif
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/*
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* Check the RCU kernel configuration parameters and print informative
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* messages about anything out of the ordinary. If you like #ifdef, you
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* will love this function.
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*/
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static void __init rcu_bootup_announce_oddness(void)
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{
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#ifdef CONFIG_RCU_TRACE
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printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
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#endif
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#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
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printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
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CONFIG_RCU_FANOUT);
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#endif
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#ifdef CONFIG_RCU_FANOUT_EXACT
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printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
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#endif
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#ifdef CONFIG_RCU_FAST_NO_HZ
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printk(KERN_INFO
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"\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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#endif
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#ifdef CONFIG_PROVE_RCU
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printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
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#endif
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#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
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printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
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#endif
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#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
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printk(KERN_INFO "\tVerbose stalled-CPUs detection is disabled.\n");
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#endif
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#if NUM_RCU_LVL_4 != 0
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printk(KERN_INFO "\tExperimental four-level hierarchy is enabled.\n");
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#endif
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}
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#ifdef CONFIG_TREE_PREEMPT_RCU
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struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt);
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DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
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static struct rcu_state *rcu_state = &rcu_preempt_state;
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static void rcu_read_unlock_special(struct task_struct *t);
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static int rcu_preempted_readers_exp(struct rcu_node *rnp);
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/*
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* Tell them what RCU they are running.
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*/
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static void __init rcu_bootup_announce(void)
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{
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printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
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rcu_bootup_announce_oddness();
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}
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/*
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* Return the number of RCU-preempt batches processed thus far
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* for debug and statistics.
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*/
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long rcu_batches_completed_preempt(void)
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{
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return rcu_preempt_state.completed;
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
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/*
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* Return the number of RCU batches processed thus far for debug & stats.
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*/
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long rcu_batches_completed(void)
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{
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return rcu_batches_completed_preempt();
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed);
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/*
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* Force a quiescent state for preemptible RCU.
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*/
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void rcu_force_quiescent_state(void)
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{
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force_quiescent_state(&rcu_preempt_state, 0);
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}
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EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU. Note
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* that this just means that the task currently running on the CPU is
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* not in a quiescent state. There might be any number of tasks blocked
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* while in an RCU read-side critical section.
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*
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* Unlike the other rcu_*_qs() functions, callers to this function
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* must disable irqs in order to protect the assignment to
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* ->rcu_read_unlock_special.
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*/
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static void rcu_preempt_qs(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
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rdp->passed_quiesce_gpnum = rdp->gpnum;
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barrier();
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if (rdp->passed_quiesce == 0)
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trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
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rdp->passed_quiesce = 1;
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current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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}
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/*
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* We have entered the scheduler, and the current task might soon be
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* context-switched away from. If this task is in an RCU read-side
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* critical section, we will no longer be able to rely on the CPU to
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* record that fact, so we enqueue the task on the blkd_tasks list.
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* The task will dequeue itself when it exits the outermost enclosing
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* RCU read-side critical section. Therefore, the current grace period
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* cannot be permitted to complete until the blkd_tasks list entries
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* predating the current grace period drain, in other words, until
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* rnp->gp_tasks becomes NULL.
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*
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* Caller must disable preemption.
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*/
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static void rcu_preempt_note_context_switch(int cpu)
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{
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struct task_struct *t = current;
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unsigned long flags;
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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if (t->rcu_read_lock_nesting > 0 &&
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(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
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/* Possibly blocking in an RCU read-side critical section. */
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rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
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rnp = rdp->mynode;
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raw_spin_lock_irqsave(&rnp->lock, flags);
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t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
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t->rcu_blocked_node = rnp;
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/*
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* If this CPU has already checked in, then this task
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* will hold up the next grace period rather than the
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* current grace period. Queue the task accordingly.
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* If the task is queued for the current grace period
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* (i.e., this CPU has not yet passed through a quiescent
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* state for the current grace period), then as long
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* as that task remains queued, the current grace period
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* cannot end. Note that there is some uncertainty as
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* to exactly when the current grace period started.
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* We take a conservative approach, which can result
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* in unnecessarily waiting on tasks that started very
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* slightly after the current grace period began. C'est
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* la vie!!!
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*
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* But first, note that the current CPU must still be
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* on line!
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*/
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WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
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WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
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list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
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rnp->gp_tasks = &t->rcu_node_entry;
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#ifdef CONFIG_RCU_BOOST
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if (rnp->boost_tasks != NULL)
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rnp->boost_tasks = rnp->gp_tasks;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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} else {
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list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
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if (rnp->qsmask & rdp->grpmask)
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rnp->gp_tasks = &t->rcu_node_entry;
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}
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trace_rcu_preempt_task(rdp->rsp->name,
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t->pid,
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(rnp->qsmask & rdp->grpmask)
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? rnp->gpnum
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: rnp->gpnum + 1);
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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} else if (t->rcu_read_lock_nesting < 0 &&
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t->rcu_read_unlock_special) {
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/*
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* Complete exit from RCU read-side critical section on
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* behalf of preempted instance of __rcu_read_unlock().
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*/
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rcu_read_unlock_special(t);
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}
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/*
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* Either we were not in an RCU read-side critical section to
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* begin with, or we have now recorded that critical section
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* globally. Either way, we can now note a quiescent state
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* for this CPU. Again, if we were in an RCU read-side critical
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* section, and if that critical section was blocking the current
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* grace period, then the fact that the task has been enqueued
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* means that we continue to block the current grace period.
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*/
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local_irq_save(flags);
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rcu_preempt_qs(cpu);
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local_irq_restore(flags);
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}
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/*
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* Tree-preemptible RCU implementation for rcu_read_lock().
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* Just increment ->rcu_read_lock_nesting, shared state will be updated
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* if we block.
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*/
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void __rcu_read_lock(void)
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{
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current->rcu_read_lock_nesting++;
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barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
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}
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EXPORT_SYMBOL_GPL(__rcu_read_lock);
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/*
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* Check for preempted RCU readers blocking the current grace period
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* for the specified rcu_node structure. If the caller needs a reliable
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* answer, it must hold the rcu_node's ->lock.
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*/
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static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
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{
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return rnp->gp_tasks != NULL;
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}
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/*
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* Record a quiescent state for all tasks that were previously queued
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* on the specified rcu_node structure and that were blocking the current
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* RCU grace period. The caller must hold the specified rnp->lock with
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* irqs disabled, and this lock is released upon return, but irqs remain
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* disabled.
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*/
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static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
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__releases(rnp->lock)
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{
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unsigned long mask;
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struct rcu_node *rnp_p;
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if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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return; /* Still need more quiescent states! */
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}
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rnp_p = rnp->parent;
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if (rnp_p == NULL) {
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/*
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* Either there is only one rcu_node in the tree,
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* or tasks were kicked up to root rcu_node due to
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* CPUs going offline.
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*/
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rcu_report_qs_rsp(&rcu_preempt_state, flags);
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return;
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}
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/* Report up the rest of the hierarchy. */
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mask = rnp->grpmask;
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
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rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
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}
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/*
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* Advance a ->blkd_tasks-list pointer to the next entry, instead
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* returning NULL if at the end of the list.
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*/
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static struct list_head *rcu_next_node_entry(struct task_struct *t,
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struct rcu_node *rnp)
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{
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struct list_head *np;
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np = t->rcu_node_entry.next;
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if (np == &rnp->blkd_tasks)
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np = NULL;
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return np;
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}
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/*
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* Handle special cases during rcu_read_unlock(), such as needing to
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* notify RCU core processing or task having blocked during the RCU
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* read-side critical section.
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*/
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static noinline void rcu_read_unlock_special(struct task_struct *t)
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{
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int empty;
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int empty_exp;
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int empty_exp_now;
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unsigned long flags;
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struct list_head *np;
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#ifdef CONFIG_RCU_BOOST
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struct rt_mutex *rbmp = NULL;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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struct rcu_node *rnp;
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int special;
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/* NMI handlers cannot block and cannot safely manipulate state. */
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if (in_nmi())
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return;
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local_irq_save(flags);
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/*
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* If RCU core is waiting for this CPU to exit critical section,
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* let it know that we have done so.
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*/
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special = t->rcu_read_unlock_special;
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if (special & RCU_READ_UNLOCK_NEED_QS) {
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rcu_preempt_qs(smp_processor_id());
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}
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/* Hardware IRQ handlers cannot block. */
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if (in_irq() || in_serving_softirq()) {
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local_irq_restore(flags);
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return;
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}
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/* Clean up if blocked during RCU read-side critical section. */
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if (special & RCU_READ_UNLOCK_BLOCKED) {
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t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
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/*
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* Remove this task from the list it blocked on. The
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* task can migrate while we acquire the lock, but at
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* most one time. So at most two passes through loop.
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*/
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for (;;) {
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rnp = t->rcu_blocked_node;
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raw_spin_lock(&rnp->lock); /* irqs already disabled. */
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if (rnp == t->rcu_blocked_node)
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break;
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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}
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empty = !rcu_preempt_blocked_readers_cgp(rnp);
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empty_exp = !rcu_preempted_readers_exp(rnp);
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smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
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np = rcu_next_node_entry(t, rnp);
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list_del_init(&t->rcu_node_entry);
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t->rcu_blocked_node = NULL;
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trace_rcu_unlock_preempted_task("rcu_preempt",
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rnp->gpnum, t->pid);
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if (&t->rcu_node_entry == rnp->gp_tasks)
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rnp->gp_tasks = np;
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if (&t->rcu_node_entry == rnp->exp_tasks)
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rnp->exp_tasks = np;
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#ifdef CONFIG_RCU_BOOST
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if (&t->rcu_node_entry == rnp->boost_tasks)
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rnp->boost_tasks = np;
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/* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
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if (t->rcu_boost_mutex) {
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rbmp = t->rcu_boost_mutex;
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t->rcu_boost_mutex = NULL;
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}
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#endif /* #ifdef CONFIG_RCU_BOOST */
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/*
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* If this was the last task on the current list, and if
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* we aren't waiting on any CPUs, report the quiescent state.
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* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
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* so we must take a snapshot of the expedited state.
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*/
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empty_exp_now = !rcu_preempted_readers_exp(rnp);
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if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
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trace_rcu_quiescent_state_report("preempt_rcu",
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rnp->gpnum,
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0, rnp->qsmask,
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rnp->level,
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rnp->grplo,
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rnp->grphi,
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!!rnp->gp_tasks);
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rcu_report_unblock_qs_rnp(rnp, flags);
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} else
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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#ifdef CONFIG_RCU_BOOST
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/* Unboost if we were boosted. */
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if (rbmp)
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rt_mutex_unlock(rbmp);
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#endif /* #ifdef CONFIG_RCU_BOOST */
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/*
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* If this was the last task on the expedited lists,
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* then we need to report up the rcu_node hierarchy.
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*/
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if (!empty_exp && empty_exp_now)
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rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
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} else {
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local_irq_restore(flags);
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}
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}
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/*
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* Tree-preemptible RCU implementation for rcu_read_unlock().
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* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
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* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
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* invoke rcu_read_unlock_special() to clean up after a context switch
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* in an RCU read-side critical section and other special cases.
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*/
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void __rcu_read_unlock(void)
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{
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struct task_struct *t = current;
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if (t->rcu_read_lock_nesting != 1)
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--t->rcu_read_lock_nesting;
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else {
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barrier(); /* critical section before exit code. */
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t->rcu_read_lock_nesting = INT_MIN;
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barrier(); /* assign before ->rcu_read_unlock_special load */
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if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
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rcu_read_unlock_special(t);
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barrier(); /* ->rcu_read_unlock_special load before assign */
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t->rcu_read_lock_nesting = 0;
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}
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#ifdef CONFIG_PROVE_LOCKING
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{
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int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
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WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
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}
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#endif /* #ifdef CONFIG_PROVE_LOCKING */
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}
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EXPORT_SYMBOL_GPL(__rcu_read_unlock);
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#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
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/*
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* Dump detailed information for all tasks blocking the current RCU
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* grace period on the specified rcu_node structure.
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*/
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static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
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{
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unsigned long flags;
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struct task_struct *t;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp))
|
|
return;
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
t = list_entry(rnp->gp_tasks,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
|
|
sched_show_task(t);
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
struct rcu_node *rnp = rcu_get_root(rsp);
|
|
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
|
|
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
|
|
|
|
/*
|
|
* Scan the current list of tasks blocked within RCU read-side critical
|
|
* sections, printing out the tid of each.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
int ndetected = 0;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp))
|
|
return 0;
|
|
t = list_entry(rnp->gp_tasks,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
|
|
printk(" P%d", t->pid);
|
|
ndetected++;
|
|
}
|
|
return ndetected;
|
|
}
|
|
|
|
/*
|
|
* Suppress preemptible RCU's CPU stall warnings by pushing the
|
|
* time of the next stall-warning message comfortably far into the
|
|
* future.
|
|
*/
|
|
static void rcu_preempt_stall_reset(void)
|
|
{
|
|
rcu_preempt_state.jiffies_stall = jiffies + ULONG_MAX / 2;
|
|
}
|
|
|
|
/*
|
|
* Check that the list of blocked tasks for the newly completed grace
|
|
* period is in fact empty. It is a serious bug to complete a grace
|
|
* period that still has RCU readers blocked! This function must be
|
|
* invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
|
|
* must be held by the caller.
|
|
*
|
|
* Also, if there are blocked tasks on the list, they automatically
|
|
* block the newly created grace period, so set up ->gp_tasks accordingly.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
|
|
if (!list_empty(&rnp->blkd_tasks))
|
|
rnp->gp_tasks = rnp->blkd_tasks.next;
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Handle tasklist migration for case in which all CPUs covered by the
|
|
* specified rcu_node have gone offline. Move them up to the root
|
|
* rcu_node. The reason for not just moving them to the immediate
|
|
* parent is to remove the need for rcu_read_unlock_special() to
|
|
* make more than two attempts to acquire the target rcu_node's lock.
|
|
* Returns true if there were tasks blocking the current RCU grace
|
|
* period.
|
|
*
|
|
* Returns 1 if there was previously a task blocking the current grace
|
|
* period on the specified rcu_node structure.
|
|
*
|
|
* The caller must hold rnp->lock with irqs disabled.
|
|
*/
|
|
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
|
|
struct rcu_node *rnp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
struct list_head *lp;
|
|
struct list_head *lp_root;
|
|
int retval = 0;
|
|
struct rcu_node *rnp_root = rcu_get_root(rsp);
|
|
struct task_struct *t;
|
|
|
|
if (rnp == rnp_root) {
|
|
WARN_ONCE(1, "Last CPU thought to be offlined?");
|
|
return 0; /* Shouldn't happen: at least one CPU online. */
|
|
}
|
|
|
|
/* If we are on an internal node, complain bitterly. */
|
|
WARN_ON_ONCE(rnp != rdp->mynode);
|
|
|
|
/*
|
|
* Move tasks up to root rcu_node. Don't try to get fancy for
|
|
* this corner-case operation -- just put this node's tasks
|
|
* at the head of the root node's list, and update the root node's
|
|
* ->gp_tasks and ->exp_tasks pointers to those of this node's,
|
|
* if non-NULL. This might result in waiting for more tasks than
|
|
* absolutely necessary, but this is a good performance/complexity
|
|
* tradeoff.
|
|
*/
|
|
if (rcu_preempt_blocked_readers_cgp(rnp))
|
|
retval |= RCU_OFL_TASKS_NORM_GP;
|
|
if (rcu_preempted_readers_exp(rnp))
|
|
retval |= RCU_OFL_TASKS_EXP_GP;
|
|
lp = &rnp->blkd_tasks;
|
|
lp_root = &rnp_root->blkd_tasks;
|
|
while (!list_empty(lp)) {
|
|
t = list_entry(lp->next, typeof(*t), rcu_node_entry);
|
|
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
|
|
list_del(&t->rcu_node_entry);
|
|
t->rcu_blocked_node = rnp_root;
|
|
list_add(&t->rcu_node_entry, lp_root);
|
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
|
rnp_root->gp_tasks = rnp->gp_tasks;
|
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
|
rnp_root->exp_tasks = rnp->exp_tasks;
|
|
#ifdef CONFIG_RCU_BOOST
|
|
if (&t->rcu_node_entry == rnp->boost_tasks)
|
|
rnp_root->boost_tasks = rnp->boost_tasks;
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
/* In case root is being boosted and leaf is not. */
|
|
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
|
|
if (rnp_root->boost_tasks != NULL &&
|
|
rnp_root->boost_tasks != rnp_root->gp_tasks)
|
|
rnp_root->boost_tasks = rnp_root->gp_tasks;
|
|
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
rnp->gp_tasks = NULL;
|
|
rnp->exp_tasks = NULL;
|
|
return retval;
|
|
}
|
|
|
|
/*
|
|
* Do CPU-offline processing for preemptible RCU.
|
|
*/
|
|
static void rcu_preempt_offline_cpu(int cpu)
|
|
{
|
|
__rcu_offline_cpu(cpu, &rcu_preempt_state);
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Check for a quiescent state from the current CPU. When a task blocks,
|
|
* the task is recorded in the corresponding CPU's rcu_node structure,
|
|
* which is checked elsewhere.
|
|
*
|
|
* Caller must disable hard irqs.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(int cpu)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (t->rcu_read_lock_nesting == 0) {
|
|
rcu_preempt_qs(cpu);
|
|
return;
|
|
}
|
|
if (t->rcu_read_lock_nesting > 0 &&
|
|
per_cpu(rcu_preempt_data, cpu).qs_pending)
|
|
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
|
|
}
|
|
|
|
/*
|
|
* Process callbacks for preemptible RCU.
|
|
*/
|
|
static void rcu_preempt_process_callbacks(void)
|
|
{
|
|
__rcu_process_callbacks(&rcu_preempt_state,
|
|
&__get_cpu_var(rcu_preempt_data));
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
static void rcu_preempt_do_callbacks(void)
|
|
{
|
|
rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
/*
|
|
* Queue a preemptible-RCU callback for invocation after a grace period.
|
|
*/
|
|
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
|
|
{
|
|
__call_rcu(head, func, &rcu_preempt_state);
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu);
|
|
|
|
/**
|
|
* synchronize_rcu - wait until a grace period has elapsed.
|
|
*
|
|
* Control will return to the caller some time after a full grace
|
|
* period has elapsed, in other words after all currently executing RCU
|
|
* read-side critical sections have completed. Note, however, that
|
|
* upon return from synchronize_rcu(), the caller might well be executing
|
|
* concurrently with new RCU read-side critical sections that began while
|
|
* synchronize_rcu() was waiting. RCU read-side critical sections are
|
|
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
|
|
*/
|
|
void synchronize_rcu(void)
|
|
{
|
|
if (!rcu_scheduler_active)
|
|
return;
|
|
wait_rcu_gp(call_rcu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu);
|
|
|
|
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
|
|
static long sync_rcu_preempt_exp_count;
|
|
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
|
|
|
|
/*
|
|
* Return non-zero if there are any tasks in RCU read-side critical
|
|
* sections blocking the current preemptible-RCU expedited grace period.
|
|
* If there is no preemptible-RCU expedited grace period currently in
|
|
* progress, returns zero unconditionally.
|
|
*/
|
|
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
|
|
{
|
|
return rnp->exp_tasks != NULL;
|
|
}
|
|
|
|
/*
|
|
* return non-zero if there is no RCU expedited grace period in progress
|
|
* for the specified rcu_node structure, in other words, if all CPUs and
|
|
* tasks covered by the specified rcu_node structure have done their bit
|
|
* for the current expedited grace period. Works only for preemptible
|
|
* RCU -- other RCU implementation use other means.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex.
|
|
*/
|
|
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
|
|
{
|
|
return !rcu_preempted_readers_exp(rnp) &&
|
|
ACCESS_ONCE(rnp->expmask) == 0;
|
|
}
|
|
|
|
/*
|
|
* Report the exit from RCU read-side critical section for the last task
|
|
* that queued itself during or before the current expedited preemptible-RCU
|
|
* grace period. This event is reported either to the rcu_node structure on
|
|
* which the task was queued or to one of that rcu_node structure's ancestors,
|
|
* recursively up the tree. (Calm down, calm down, we do the recursion
|
|
* iteratively!)
|
|
*
|
|
* Most callers will set the "wake" flag, but the task initiating the
|
|
* expedited grace period need not wake itself.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex.
|
|
*/
|
|
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
|
|
bool wake)
|
|
{
|
|
unsigned long flags;
|
|
unsigned long mask;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
for (;;) {
|
|
if (!sync_rcu_preempt_exp_done(rnp)) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
break;
|
|
}
|
|
if (rnp->parent == NULL) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
if (wake)
|
|
wake_up(&sync_rcu_preempt_exp_wq);
|
|
break;
|
|
}
|
|
mask = rnp->grpmask;
|
|
raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
|
|
rnp = rnp->parent;
|
|
raw_spin_lock(&rnp->lock); /* irqs already disabled */
|
|
rnp->expmask &= ~mask;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Snapshot the tasks blocking the newly started preemptible-RCU expedited
|
|
* grace period for the specified rcu_node structure. If there are no such
|
|
* tasks, report it up the rcu_node hierarchy.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
|
|
*/
|
|
static void
|
|
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
int must_wait = 0;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
if (list_empty(&rnp->blkd_tasks))
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
else {
|
|
rnp->exp_tasks = rnp->blkd_tasks.next;
|
|
rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
|
|
must_wait = 1;
|
|
}
|
|
if (!must_wait)
|
|
rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
|
|
}
|
|
|
|
/*
|
|
* Wait for an rcu-preempt grace period, but expedite it. The basic idea
|
|
* is to invoke synchronize_sched_expedited() to push all the tasks to
|
|
* the ->blkd_tasks lists and wait for this list to drain.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp = &rcu_preempt_state;
|
|
long snap;
|
|
int trycount = 0;
|
|
|
|
smp_mb(); /* Caller's modifications seen first by other CPUs. */
|
|
snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
|
|
smp_mb(); /* Above access cannot bleed into critical section. */
|
|
|
|
/*
|
|
* Acquire lock, falling back to synchronize_rcu() if too many
|
|
* lock-acquisition failures. Of course, if someone does the
|
|
* expedited grace period for us, just leave.
|
|
*/
|
|
while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
|
|
if (trycount++ < 10)
|
|
udelay(trycount * num_online_cpus());
|
|
else {
|
|
synchronize_rcu();
|
|
return;
|
|
}
|
|
if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
|
|
goto mb_ret; /* Others did our work for us. */
|
|
}
|
|
if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
|
|
goto unlock_mb_ret; /* Others did our work for us. */
|
|
|
|
/* force all RCU readers onto ->blkd_tasks lists. */
|
|
synchronize_sched_expedited();
|
|
|
|
raw_spin_lock_irqsave(&rsp->onofflock, flags);
|
|
|
|
/* Initialize ->expmask for all non-leaf rcu_node structures. */
|
|
rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
|
|
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
|
|
rnp->expmask = rnp->qsmaskinit;
|
|
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
|
|
}
|
|
|
|
/* Snapshot current state of ->blkd_tasks lists. */
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
sync_rcu_preempt_exp_init(rsp, rnp);
|
|
if (NUM_RCU_NODES > 1)
|
|
sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
|
|
|
|
raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
|
|
|
|
/* Wait for snapshotted ->blkd_tasks lists to drain. */
|
|
rnp = rcu_get_root(rsp);
|
|
wait_event(sync_rcu_preempt_exp_wq,
|
|
sync_rcu_preempt_exp_done(rnp));
|
|
|
|
/* Clean up and exit. */
|
|
smp_mb(); /* ensure expedited GP seen before counter increment. */
|
|
ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
|
|
unlock_mb_ret:
|
|
mutex_unlock(&sync_rcu_preempt_exp_mutex);
|
|
mb_ret:
|
|
smp_mb(); /* ensure subsequent action seen after grace period. */
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
/*
|
|
* Check to see if there is any immediate preemptible-RCU-related work
|
|
* to be done.
|
|
*/
|
|
static int rcu_preempt_pending(int cpu)
|
|
{
|
|
return __rcu_pending(&rcu_preempt_state,
|
|
&per_cpu(rcu_preempt_data, cpu));
|
|
}
|
|
|
|
/*
|
|
* Does preemptible RCU need the CPU to stay out of dynticks mode?
|
|
*/
|
|
static int rcu_preempt_needs_cpu(int cpu)
|
|
{
|
|
return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
|
|
}
|
|
|
|
/**
|
|
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
_rcu_barrier(&rcu_preempt_state, call_rcu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Initialize preemptible RCU's per-CPU data.
|
|
*/
|
|
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
|
|
{
|
|
rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
|
|
}
|
|
|
|
/*
|
|
* Move preemptible RCU's callbacks from dying CPU to other online CPU.
|
|
*/
|
|
static void rcu_preempt_send_cbs_to_online(void)
|
|
{
|
|
rcu_send_cbs_to_online(&rcu_preempt_state);
|
|
}
|
|
|
|
/*
|
|
* Initialize preemptible RCU's state structures.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
|
|
}
|
|
|
|
/*
|
|
* Check for a task exiting while in a preemptible-RCU read-side
|
|
* critical section, clean up if so. No need to issue warnings,
|
|
* as debug_check_no_locks_held() already does this if lockdep
|
|
* is enabled.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (t->rcu_read_lock_nesting == 0)
|
|
return;
|
|
t->rcu_read_lock_nesting = 1;
|
|
__rcu_read_unlock();
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
static struct rcu_state *rcu_state = &rcu_sched_state;
|
|
|
|
/*
|
|
* Tell them what RCU they are running.
|
|
*/
|
|
static void __init rcu_bootup_announce(void)
|
|
{
|
|
printk(KERN_INFO "Hierarchical RCU implementation.\n");
|
|
rcu_bootup_announce_oddness();
|
|
}
|
|
|
|
/*
|
|
* Return the number of RCU batches processed thus far for debug & stats.
|
|
*/
|
|
long rcu_batches_completed(void)
|
|
{
|
|
return rcu_batches_completed_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_batches_completed);
|
|
|
|
/*
|
|
* Force a quiescent state for RCU, which, because there is no preemptible
|
|
* RCU, becomes the same as rcu-sched.
|
|
*/
|
|
void rcu_force_quiescent_state(void)
|
|
{
|
|
rcu_sched_force_quiescent_state();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* CPUs being in quiescent states.
|
|
*/
|
|
static void rcu_preempt_note_context_switch(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there are never any preempted
|
|
* RCU readers.
|
|
*/
|
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/* Because preemptible RCU does not exist, no quieting of tasks. */
|
|
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there is no need to suppress
|
|
* its CPU stall warnings.
|
|
*/
|
|
static void rcu_preempt_stall_reset(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked,
|
|
* so there is no need to check for blocked tasks. So check only for
|
|
* bogus qsmask values.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never needs to migrate
|
|
* tasks that were blocked within RCU read-side critical sections, and
|
|
* such non-existent tasks cannot possibly have been blocking the current
|
|
* grace period.
|
|
*/
|
|
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
|
|
struct rcu_node *rnp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never needs CPU-offline
|
|
* processing.
|
|
*/
|
|
static void rcu_preempt_offline_cpu(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to check.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to process.
|
|
*/
|
|
static void rcu_preempt_process_callbacks(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Wait for an rcu-preempt grace period, but make it happen quickly.
|
|
* But because preemptible RCU does not exist, map to rcu-sched.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
synchronize_sched_expedited();
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there is never any need to
|
|
* report on tasks preempted in RCU read-side critical sections during
|
|
* expedited RCU grace periods.
|
|
*/
|
|
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
|
|
bool wake)
|
|
{
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any work to do.
|
|
*/
|
|
static int rcu_preempt_pending(int cpu)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never needs any CPU.
|
|
*/
|
|
static int rcu_preempt_needs_cpu(int cpu)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, rcu_barrier() is just
|
|
* another name for rcu_barrier_sched().
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
rcu_barrier_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there is no per-CPU
|
|
* data to initialize.
|
|
*/
|
|
static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there are no callbacks to move.
|
|
*/
|
|
static void rcu_preempt_send_cbs_to_online(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it need not be initialized.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
#include "rtmutex_common.h"
|
|
|
|
#ifdef CONFIG_RCU_TRACE
|
|
|
|
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
|
|
{
|
|
if (list_empty(&rnp->blkd_tasks))
|
|
rnp->n_balk_blkd_tasks++;
|
|
else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
|
|
rnp->n_balk_exp_gp_tasks++;
|
|
else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
|
|
rnp->n_balk_boost_tasks++;
|
|
else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
|
|
rnp->n_balk_notblocked++;
|
|
else if (rnp->gp_tasks != NULL &&
|
|
ULONG_CMP_LT(jiffies, rnp->boost_time))
|
|
rnp->n_balk_notyet++;
|
|
else
|
|
rnp->n_balk_nos++;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_TRACE */
|
|
|
|
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_TRACE */
|
|
|
|
static struct lock_class_key rcu_boost_class;
|
|
|
|
/*
|
|
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
|
|
* or ->boost_tasks, advancing the pointer to the next task in the
|
|
* ->blkd_tasks list.
|
|
*
|
|
* Note that irqs must be enabled: boosting the task can block.
|
|
* Returns 1 if there are more tasks needing to be boosted.
|
|
*/
|
|
static int rcu_boost(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct rt_mutex mtx;
|
|
struct task_struct *t;
|
|
struct list_head *tb;
|
|
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
|
|
return 0; /* Nothing left to boost. */
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
|
|
/*
|
|
* Recheck under the lock: all tasks in need of boosting
|
|
* might exit their RCU read-side critical sections on their own.
|
|
*/
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Preferentially boost tasks blocking expedited grace periods.
|
|
* This cannot starve the normal grace periods because a second
|
|
* expedited grace period must boost all blocked tasks, including
|
|
* those blocking the pre-existing normal grace period.
|
|
*/
|
|
if (rnp->exp_tasks != NULL) {
|
|
tb = rnp->exp_tasks;
|
|
rnp->n_exp_boosts++;
|
|
} else {
|
|
tb = rnp->boost_tasks;
|
|
rnp->n_normal_boosts++;
|
|
}
|
|
rnp->n_tasks_boosted++;
|
|
|
|
/*
|
|
* We boost task t by manufacturing an rt_mutex that appears to
|
|
* be held by task t. We leave a pointer to that rt_mutex where
|
|
* task t can find it, and task t will release the mutex when it
|
|
* exits its outermost RCU read-side critical section. Then
|
|
* simply acquiring this artificial rt_mutex will boost task
|
|
* t's priority. (Thanks to tglx for suggesting this approach!)
|
|
*
|
|
* Note that task t must acquire rnp->lock to remove itself from
|
|
* the ->blkd_tasks list, which it will do from exit() if from
|
|
* nowhere else. We therefore are guaranteed that task t will
|
|
* stay around at least until we drop rnp->lock. Note that
|
|
* rnp->lock also resolves races between our priority boosting
|
|
* and task t's exiting its outermost RCU read-side critical
|
|
* section.
|
|
*/
|
|
t = container_of(tb, struct task_struct, rcu_node_entry);
|
|
rt_mutex_init_proxy_locked(&mtx, t);
|
|
/* Avoid lockdep false positives. This rt_mutex is its own thing. */
|
|
lockdep_set_class_and_name(&mtx.wait_lock, &rcu_boost_class,
|
|
"rcu_boost_mutex");
|
|
t->rcu_boost_mutex = &mtx;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
|
|
rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
|
|
|
|
return rnp->exp_tasks != NULL || rnp->boost_tasks != NULL;
|
|
}
|
|
|
|
/*
|
|
* Timer handler to initiate waking up of boost kthreads that
|
|
* have yielded the CPU due to excessive numbers of tasks to
|
|
* boost. We wake up the per-rcu_node kthread, which in turn
|
|
* will wake up the booster kthread.
|
|
*/
|
|
static void rcu_boost_kthread_timer(unsigned long arg)
|
|
{
|
|
invoke_rcu_node_kthread((struct rcu_node *)arg);
|
|
}
|
|
|
|
/*
|
|
* Priority-boosting kthread. One per leaf rcu_node and one for the
|
|
* root rcu_node.
|
|
*/
|
|
static int rcu_boost_kthread(void *arg)
|
|
{
|
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
|
int spincnt = 0;
|
|
int more2boost;
|
|
|
|
trace_rcu_utilization("Start boost kthread@init");
|
|
for (;;) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
|
|
trace_rcu_utilization("End boost kthread@rcu_wait");
|
|
rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
|
|
trace_rcu_utilization("Start boost kthread@rcu_wait");
|
|
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
|
|
more2boost = rcu_boost(rnp);
|
|
if (more2boost)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
trace_rcu_utilization("End boost kthread@rcu_yield");
|
|
rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp);
|
|
trace_rcu_utilization("Start boost kthread@rcu_yield");
|
|
spincnt = 0;
|
|
}
|
|
}
|
|
/* NOTREACHED */
|
|
trace_rcu_utilization("End boost kthread@notreached");
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Check to see if it is time to start boosting RCU readers that are
|
|
* blocking the current grace period, and, if so, tell the per-rcu_node
|
|
* kthread to start boosting them. If there is an expedited grace
|
|
* period in progress, it is always time to boost.
|
|
*
|
|
* The caller must hold rnp->lock, which this function releases,
|
|
* but irqs remain disabled. The ->boost_kthread_task is immortal,
|
|
* so we don't need to worry about it going away.
|
|
*/
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
|
|
rnp->n_balk_exp_gp_tasks++;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
return;
|
|
}
|
|
if (rnp->exp_tasks != NULL ||
|
|
(rnp->gp_tasks != NULL &&
|
|
rnp->boost_tasks == NULL &&
|
|
rnp->qsmask == 0 &&
|
|
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
|
|
if (rnp->exp_tasks == NULL)
|
|
rnp->boost_tasks = rnp->gp_tasks;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
t = rnp->boost_kthread_task;
|
|
if (t != NULL)
|
|
wake_up_process(t);
|
|
} else {
|
|
rcu_initiate_boost_trace(rnp);
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Wake up the per-CPU kthread to invoke RCU callbacks.
|
|
*/
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
local_irq_save(flags);
|
|
__this_cpu_write(rcu_cpu_has_work, 1);
|
|
if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
|
|
current != __this_cpu_read(rcu_cpu_kthread_task))
|
|
wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/*
|
|
* Set the affinity of the boost kthread. The CPU-hotplug locks are
|
|
* held, so no one should be messing with the existence of the boost
|
|
* kthread.
|
|
*/
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
|
|
cpumask_var_t cm)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
t = rnp->boost_kthread_task;
|
|
if (t != NULL)
|
|
set_cpus_allowed_ptr(rnp->boost_kthread_task, cm);
|
|
}
|
|
|
|
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
|
|
|
|
/*
|
|
* Do priority-boost accounting for the start of a new grace period.
|
|
*/
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
|
|
}
|
|
|
|
/*
|
|
* Create an RCU-boost kthread for the specified node if one does not
|
|
* already exist. We only create this kthread for preemptible RCU.
|
|
* Returns zero if all is well, a negated errno otherwise.
|
|
*/
|
|
static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
|
|
struct rcu_node *rnp,
|
|
int rnp_index)
|
|
{
|
|
unsigned long flags;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (&rcu_preempt_state != rsp)
|
|
return 0;
|
|
rsp->boost = 1;
|
|
if (rnp->boost_kthread_task != NULL)
|
|
return 0;
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
|
"rcub/%d", rnp_index);
|
|
if (IS_ERR(t))
|
|
return PTR_ERR(t);
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
rnp->boost_kthread_task = t;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
sp.sched_priority = RCU_BOOST_PRIO;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
return 0;
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Stop the RCU's per-CPU kthread when its CPU goes offline,.
|
|
*/
|
|
static void rcu_stop_cpu_kthread(int cpu)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
/* Stop the CPU's kthread. */
|
|
t = per_cpu(rcu_cpu_kthread_task, cpu);
|
|
if (t != NULL) {
|
|
per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
|
|
kthread_stop(t);
|
|
}
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
static void rcu_kthread_do_work(void)
|
|
{
|
|
rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
|
|
rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
|
|
rcu_preempt_do_callbacks();
|
|
}
|
|
|
|
/*
|
|
* Wake up the specified per-rcu_node-structure kthread.
|
|
* Because the per-rcu_node kthreads are immortal, we don't need
|
|
* to do anything to keep them alive.
|
|
*/
|
|
static void invoke_rcu_node_kthread(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
t = rnp->node_kthread_task;
|
|
if (t != NULL)
|
|
wake_up_process(t);
|
|
}
|
|
|
|
/*
|
|
* Set the specified CPU's kthread to run RT or not, as specified by
|
|
* the to_rt argument. The CPU-hotplug locks are held, so the task
|
|
* is not going away.
|
|
*/
|
|
static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
|
|
{
|
|
int policy;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
t = per_cpu(rcu_cpu_kthread_task, cpu);
|
|
if (t == NULL)
|
|
return;
|
|
if (to_rt) {
|
|
policy = SCHED_FIFO;
|
|
sp.sched_priority = RCU_KTHREAD_PRIO;
|
|
} else {
|
|
policy = SCHED_NORMAL;
|
|
sp.sched_priority = 0;
|
|
}
|
|
sched_setscheduler_nocheck(t, policy, &sp);
|
|
}
|
|
|
|
/*
|
|
* Timer handler to initiate the waking up of per-CPU kthreads that
|
|
* have yielded the CPU due to excess numbers of RCU callbacks.
|
|
* We wake up the per-rcu_node kthread, which in turn will wake up
|
|
* the booster kthread.
|
|
*/
|
|
static void rcu_cpu_kthread_timer(unsigned long arg)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
atomic_or(rdp->grpmask, &rnp->wakemask);
|
|
invoke_rcu_node_kthread(rnp);
|
|
}
|
|
|
|
/*
|
|
* Drop to non-real-time priority and yield, but only after posting a
|
|
* timer that will cause us to regain our real-time priority if we
|
|
* remain preempted. Either way, we restore our real-time priority
|
|
* before returning.
|
|
*/
|
|
static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
|
|
{
|
|
struct sched_param sp;
|
|
struct timer_list yield_timer;
|
|
int prio = current->rt_priority;
|
|
|
|
setup_timer_on_stack(&yield_timer, f, arg);
|
|
mod_timer(&yield_timer, jiffies + 2);
|
|
sp.sched_priority = 0;
|
|
sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
|
|
set_user_nice(current, 19);
|
|
schedule();
|
|
set_user_nice(current, 0);
|
|
sp.sched_priority = prio;
|
|
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
|
|
del_timer(&yield_timer);
|
|
}
|
|
|
|
/*
|
|
* Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
|
|
* This can happen while the corresponding CPU is either coming online
|
|
* or going offline. We cannot wait until the CPU is fully online
|
|
* before starting the kthread, because the various notifier functions
|
|
* can wait for RCU grace periods. So we park rcu_cpu_kthread() until
|
|
* the corresponding CPU is online.
|
|
*
|
|
* Return 1 if the kthread needs to stop, 0 otherwise.
|
|
*
|
|
* Caller must disable bh. This function can momentarily enable it.
|
|
*/
|
|
static int rcu_cpu_kthread_should_stop(int cpu)
|
|
{
|
|
while (cpu_is_offline(cpu) ||
|
|
!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) ||
|
|
smp_processor_id() != cpu) {
|
|
if (kthread_should_stop())
|
|
return 1;
|
|
per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
|
|
per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
|
|
local_bh_enable();
|
|
schedule_timeout_uninterruptible(1);
|
|
if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)))
|
|
set_cpus_allowed_ptr(current, cpumask_of(cpu));
|
|
local_bh_disable();
|
|
}
|
|
per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Per-CPU kernel thread that invokes RCU callbacks. This replaces the
|
|
* RCU softirq used in flavors and configurations of RCU that do not
|
|
* support RCU priority boosting.
|
|
*/
|
|
static int rcu_cpu_kthread(void *arg)
|
|
{
|
|
int cpu = (int)(long)arg;
|
|
unsigned long flags;
|
|
int spincnt = 0;
|
|
unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
|
|
char work;
|
|
char *workp = &per_cpu(rcu_cpu_has_work, cpu);
|
|
|
|
trace_rcu_utilization("Start CPU kthread@init");
|
|
for (;;) {
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
trace_rcu_utilization("End CPU kthread@rcu_wait");
|
|
rcu_wait(*workp != 0 || kthread_should_stop());
|
|
trace_rcu_utilization("Start CPU kthread@rcu_wait");
|
|
local_bh_disable();
|
|
if (rcu_cpu_kthread_should_stop(cpu)) {
|
|
local_bh_enable();
|
|
break;
|
|
}
|
|
*statusp = RCU_KTHREAD_RUNNING;
|
|
per_cpu(rcu_cpu_kthread_loops, cpu)++;
|
|
local_irq_save(flags);
|
|
work = *workp;
|
|
*workp = 0;
|
|
local_irq_restore(flags);
|
|
if (work)
|
|
rcu_kthread_do_work();
|
|
local_bh_enable();
|
|
if (*workp != 0)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
*statusp = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization("End CPU kthread@rcu_yield");
|
|
rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
|
|
trace_rcu_utilization("Start CPU kthread@rcu_yield");
|
|
spincnt = 0;
|
|
}
|
|
}
|
|
*statusp = RCU_KTHREAD_STOPPED;
|
|
trace_rcu_utilization("End CPU kthread@term");
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Spawn a per-CPU kthread, setting up affinity and priority.
|
|
* Because the CPU hotplug lock is held, no other CPU will be attempting
|
|
* to manipulate rcu_cpu_kthread_task. There might be another CPU
|
|
* attempting to access it during boot, but the locking in kthread_bind()
|
|
* will enforce sufficient ordering.
|
|
*
|
|
* Please note that we cannot simply refuse to wake up the per-CPU
|
|
* kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
|
|
* which can result in softlockup complaints if the task ends up being
|
|
* idle for more than a couple of minutes.
|
|
*
|
|
* However, please note also that we cannot bind the per-CPU kthread to its
|
|
* CPU until that CPU is fully online. We also cannot wait until the
|
|
* CPU is fully online before we create its per-CPU kthread, as this would
|
|
* deadlock the system when CPU notifiers tried waiting for grace
|
|
* periods. So we bind the per-CPU kthread to its CPU only if the CPU
|
|
* is online. If its CPU is not yet fully online, then the code in
|
|
* rcu_cpu_kthread() will wait until it is fully online, and then do
|
|
* the binding.
|
|
*/
|
|
static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
|
|
{
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (!rcu_scheduler_fully_active ||
|
|
per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
|
|
return 0;
|
|
t = kthread_create_on_node(rcu_cpu_kthread,
|
|
(void *)(long)cpu,
|
|
cpu_to_node(cpu),
|
|
"rcuc/%d", cpu);
|
|
if (IS_ERR(t))
|
|
return PTR_ERR(t);
|
|
if (cpu_online(cpu))
|
|
kthread_bind(t, cpu);
|
|
per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
|
|
WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
|
|
sp.sched_priority = RCU_KTHREAD_PRIO;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
per_cpu(rcu_cpu_kthread_task, cpu) = t;
|
|
wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Per-rcu_node kthread, which is in charge of waking up the per-CPU
|
|
* kthreads when needed. We ignore requests to wake up kthreads
|
|
* for offline CPUs, which is OK because force_quiescent_state()
|
|
* takes care of this case.
|
|
*/
|
|
static int rcu_node_kthread(void *arg)
|
|
{
|
|
int cpu;
|
|
unsigned long flags;
|
|
unsigned long mask;
|
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
for (;;) {
|
|
rnp->node_kthread_status = RCU_KTHREAD_WAITING;
|
|
rcu_wait(atomic_read(&rnp->wakemask) != 0);
|
|
rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
mask = atomic_xchg(&rnp->wakemask, 0);
|
|
rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
|
|
if ((mask & 0x1) == 0)
|
|
continue;
|
|
preempt_disable();
|
|
t = per_cpu(rcu_cpu_kthread_task, cpu);
|
|
if (!cpu_online(cpu) || t == NULL) {
|
|
preempt_enable();
|
|
continue;
|
|
}
|
|
per_cpu(rcu_cpu_has_work, cpu) = 1;
|
|
sp.sched_priority = RCU_KTHREAD_PRIO;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
preempt_enable();
|
|
}
|
|
}
|
|
/* NOTREACHED */
|
|
rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
|
* served by the rcu_node in question. The CPU hotplug lock is still
|
|
* held, so the value of rnp->qsmaskinit will be stable.
|
|
*
|
|
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
|
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
|
* this function allows the kthread to execute on any CPU.
|
|
*/
|
|
static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
cpumask_var_t cm;
|
|
int cpu;
|
|
unsigned long mask = rnp->qsmaskinit;
|
|
|
|
if (rnp->node_kthread_task == NULL)
|
|
return;
|
|
if (!alloc_cpumask_var(&cm, GFP_KERNEL))
|
|
return;
|
|
cpumask_clear(cm);
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
|
|
if ((mask & 0x1) && cpu != outgoingcpu)
|
|
cpumask_set_cpu(cpu, cm);
|
|
if (cpumask_weight(cm) == 0) {
|
|
cpumask_setall(cm);
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
|
|
cpumask_clear_cpu(cpu, cm);
|
|
WARN_ON_ONCE(cpumask_weight(cm) == 0);
|
|
}
|
|
set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
|
|
rcu_boost_kthread_setaffinity(rnp, cm);
|
|
free_cpumask_var(cm);
|
|
}
|
|
|
|
/*
|
|
* Spawn a per-rcu_node kthread, setting priority and affinity.
|
|
* Called during boot before online/offline can happen, or, if
|
|
* during runtime, with the main CPU-hotplug locks held. So only
|
|
* one of these can be executing at a time.
|
|
*/
|
|
static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
|
|
struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
int rnp_index = rnp - &rsp->node[0];
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (!rcu_scheduler_fully_active ||
|
|
rnp->qsmaskinit == 0)
|
|
return 0;
|
|
if (rnp->node_kthread_task == NULL) {
|
|
t = kthread_create(rcu_node_kthread, (void *)rnp,
|
|
"rcun/%d", rnp_index);
|
|
if (IS_ERR(t))
|
|
return PTR_ERR(t);
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
rnp->node_kthread_task = t;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
sp.sched_priority = 99;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
}
|
|
return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
|
|
}
|
|
|
|
/*
|
|
* Spawn all kthreads -- called as soon as the scheduler is running.
|
|
*/
|
|
static int __init rcu_spawn_kthreads(void)
|
|
{
|
|
int cpu;
|
|
struct rcu_node *rnp;
|
|
|
|
rcu_scheduler_fully_active = 1;
|
|
for_each_possible_cpu(cpu) {
|
|
per_cpu(rcu_cpu_has_work, cpu) = 0;
|
|
if (cpu_online(cpu))
|
|
(void)rcu_spawn_one_cpu_kthread(cpu);
|
|
}
|
|
rnp = rcu_get_root(rcu_state);
|
|
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
|
|
if (NUM_RCU_NODES > 1) {
|
|
rcu_for_each_leaf_node(rcu_state, rnp)
|
|
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
|
|
}
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_spawn_kthreads);
|
|
|
|
static void __cpuinit rcu_prepare_kthreads(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
|
|
if (rcu_scheduler_fully_active) {
|
|
(void)rcu_spawn_one_cpu_kthread(cpu);
|
|
if (rnp->node_kthread_task == NULL)
|
|
(void)rcu_spawn_one_node_kthread(rcu_state, rnp);
|
|
}
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
WARN_ON_ONCE(1);
|
|
}
|
|
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
static void rcu_stop_cpu_kthread(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
}
|
|
|
|
static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
|
|
{
|
|
}
|
|
|
|
static int __init rcu_scheduler_really_started(void)
|
|
{
|
|
rcu_scheduler_fully_active = 1;
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_scheduler_really_started);
|
|
|
|
static void __cpuinit rcu_prepare_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
#ifndef CONFIG_SMP
|
|
|
|
void synchronize_sched_expedited(void)
|
|
{
|
|
cond_resched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
|
|
|
|
#else /* #ifndef CONFIG_SMP */
|
|
|
|
static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
|
|
static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
|
|
|
|
static int synchronize_sched_expedited_cpu_stop(void *data)
|
|
{
|
|
/*
|
|
* There must be a full memory barrier on each affected CPU
|
|
* between the time that try_stop_cpus() is called and the
|
|
* time that it returns.
|
|
*
|
|
* In the current initial implementation of cpu_stop, the
|
|
* above condition is already met when the control reaches
|
|
* this point and the following smp_mb() is not strictly
|
|
* necessary. Do smp_mb() anyway for documentation and
|
|
* robustness against future implementation changes.
|
|
*/
|
|
smp_mb(); /* See above comment block. */
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Wait for an rcu-sched grace period to elapse, but use "big hammer"
|
|
* approach to force grace period to end quickly. This consumes
|
|
* significant time on all CPUs, and is thus not recommended for
|
|
* any sort of common-case code.
|
|
*
|
|
* Note that it is illegal to call this function while holding any
|
|
* lock that is acquired by a CPU-hotplug notifier. Failing to
|
|
* observe this restriction will result in deadlock.
|
|
*
|
|
* This implementation can be thought of as an application of ticket
|
|
* locking to RCU, with sync_sched_expedited_started and
|
|
* sync_sched_expedited_done taking on the roles of the halves
|
|
* of the ticket-lock word. Each task atomically increments
|
|
* sync_sched_expedited_started upon entry, snapshotting the old value,
|
|
* then attempts to stop all the CPUs. If this succeeds, then each
|
|
* CPU will have executed a context switch, resulting in an RCU-sched
|
|
* grace period. We are then done, so we use atomic_cmpxchg() to
|
|
* update sync_sched_expedited_done to match our snapshot -- but
|
|
* only if someone else has not already advanced past our snapshot.
|
|
*
|
|
* On the other hand, if try_stop_cpus() fails, we check the value
|
|
* of sync_sched_expedited_done. If it has advanced past our
|
|
* initial snapshot, then someone else must have forced a grace period
|
|
* some time after we took our snapshot. In this case, our work is
|
|
* done for us, and we can simply return. Otherwise, we try again,
|
|
* but keep our initial snapshot for purposes of checking for someone
|
|
* doing our work for us.
|
|
*
|
|
* If we fail too many times in a row, we fall back to synchronize_sched().
|
|
*/
|
|
void synchronize_sched_expedited(void)
|
|
{
|
|
int firstsnap, s, snap, trycount = 0;
|
|
|
|
/* Note that atomic_inc_return() implies full memory barrier. */
|
|
firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
|
|
get_online_cpus();
|
|
|
|
/*
|
|
* Each pass through the following loop attempts to force a
|
|
* context switch on each CPU.
|
|
*/
|
|
while (try_stop_cpus(cpu_online_mask,
|
|
synchronize_sched_expedited_cpu_stop,
|
|
NULL) == -EAGAIN) {
|
|
put_online_cpus();
|
|
|
|
/* No joy, try again later. Or just synchronize_sched(). */
|
|
if (trycount++ < 10)
|
|
udelay(trycount * num_online_cpus());
|
|
else {
|
|
synchronize_sched();
|
|
return;
|
|
}
|
|
|
|
/* Check to see if someone else did our work for us. */
|
|
s = atomic_read(&sync_sched_expedited_done);
|
|
if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
|
|
smp_mb(); /* ensure test happens before caller kfree */
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Refetching sync_sched_expedited_started allows later
|
|
* callers to piggyback on our grace period. We subtract
|
|
* 1 to get the same token that the last incrementer got.
|
|
* We retry after they started, so our grace period works
|
|
* for them, and they started after our first try, so their
|
|
* grace period works for us.
|
|
*/
|
|
get_online_cpus();
|
|
snap = atomic_read(&sync_sched_expedited_started);
|
|
smp_mb(); /* ensure read is before try_stop_cpus(). */
|
|
}
|
|
|
|
/*
|
|
* Everyone up to our most recent fetch is covered by our grace
|
|
* period. Update the counter, but only if our work is still
|
|
* relevant -- which it won't be if someone who started later
|
|
* than we did beat us to the punch.
|
|
*/
|
|
do {
|
|
s = atomic_read(&sync_sched_expedited_done);
|
|
if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
|
|
smp_mb(); /* ensure test happens before caller kfree */
|
|
break;
|
|
}
|
|
} while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
|
|
|
|
put_online_cpus();
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
|
|
|
|
#endif /* #else #ifndef CONFIG_SMP */
|
|
|
|
#if !defined(CONFIG_RCU_FAST_NO_HZ)
|
|
|
|
/*
|
|
* Check to see if any future RCU-related work will need to be done
|
|
* by the current CPU, even if none need be done immediately, returning
|
|
* 1 if so. This function is part of the RCU implementation; it is -not-
|
|
* an exported member of the RCU API.
|
|
*
|
|
* Because we have preemptible RCU, just check whether this CPU needs
|
|
* any flavor of RCU. Do not chew up lots of CPU cycles with preemption
|
|
* disabled in a most-likely vain attempt to cause RCU not to need this CPU.
|
|
*/
|
|
int rcu_needs_cpu(int cpu)
|
|
{
|
|
return rcu_cpu_has_callbacks(cpu);
|
|
}
|
|
|
|
/*
|
|
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=y,
|
|
* is nothing.
|
|
*/
|
|
static void rcu_prepare_for_idle(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* CPUs are never putting themselves to sleep with callbacks pending,
|
|
* so there is no need to awaken them.
|
|
*/
|
|
static void rcu_wake_cpus_for_gp_end(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* CPUs are never putting themselves to sleep with callbacks pending,
|
|
* so there is no need to schedule the act of awakening them.
|
|
*/
|
|
static void rcu_schedule_wake_gp_end(void)
|
|
{
|
|
}
|
|
|
|
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
#define RCU_NEEDS_CPU_FLUSHES 5
|
|
static DEFINE_PER_CPU(int, rcu_dyntick_drain);
|
|
static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
|
|
static DEFINE_PER_CPU(bool, rcu_awake_at_gp_end);
|
|
|
|
/*
|
|
* Allow the CPU to enter dyntick-idle mode if either: (1) There are no
|
|
* callbacks on this CPU, (2) this CPU has not yet attempted to enter
|
|
* dyntick-idle mode, or (3) this CPU is in the process of attempting to
|
|
* enter dyntick-idle mode. Otherwise, if we have recently tried and failed
|
|
* to enter dyntick-idle mode, we refuse to try to enter it. After all,
|
|
* it is better to incur scheduling-clock interrupts than to spin
|
|
* continuously for the same time duration!
|
|
*/
|
|
int rcu_needs_cpu(int cpu)
|
|
{
|
|
/* If no callbacks, RCU doesn't need the CPU. */
|
|
if (!rcu_cpu_has_callbacks(cpu))
|
|
return 0;
|
|
/* Otherwise, RCU needs the CPU only if it recently tried and failed. */
|
|
return per_cpu(rcu_dyntick_holdoff, cpu) == jiffies;
|
|
}
|
|
|
|
/*
|
|
* Check to see if any RCU-related work can be done by the current CPU,
|
|
* and if so, schedule a softirq to get it done. This function is part
|
|
* of the RCU implementation; it is -not- an exported member of the RCU API.
|
|
*
|
|
* The idea is for the current CPU to clear out all work required by the
|
|
* RCU core for the current grace period, so that this CPU can be permitted
|
|
* to enter dyntick-idle mode. In some cases, it will need to be awakened
|
|
* at the end of the grace period by whatever CPU ends the grace period.
|
|
* This allows CPUs to go dyntick-idle more quickly, and to reduce the
|
|
* number of wakeups by a modest integer factor.
|
|
*
|
|
* Because it is not legal to invoke rcu_process_callbacks() with irqs
|
|
* disabled, we do one pass of force_quiescent_state(), then do a
|
|
* invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
|
|
* later. The per-cpu rcu_dyntick_drain variable controls the sequencing.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_prepare_for_idle(int cpu)
|
|
{
|
|
int c = 0;
|
|
|
|
/* If no callbacks or in the holdoff period, enter dyntick-idle. */
|
|
if (!rcu_cpu_has_callbacks(cpu)) {
|
|
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
|
|
trace_rcu_prep_idle("No callbacks");
|
|
return;
|
|
}
|
|
if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) {
|
|
trace_rcu_prep_idle("In holdoff");
|
|
return;
|
|
}
|
|
|
|
/* Check and update the rcu_dyntick_drain sequencing. */
|
|
if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
|
|
/* First time through, initialize the counter. */
|
|
per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES;
|
|
} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
|
|
/* We have hit the limit, so time to give up. */
|
|
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
|
|
if (!rcu_pending(cpu)) {
|
|
trace_rcu_prep_idle("Dyntick with callbacks");
|
|
per_cpu(rcu_awake_at_gp_end, cpu) = 1;
|
|
return; /* Nothing to do immediately. */
|
|
}
|
|
trace_rcu_prep_idle("Begin holdoff");
|
|
invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Do one step of pushing the remaining RCU callbacks through
|
|
* the RCU core state machine.
|
|
*/
|
|
#ifdef CONFIG_TREE_PREEMPT_RCU
|
|
if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
|
|
rcu_preempt_qs(cpu);
|
|
force_quiescent_state(&rcu_preempt_state, 0);
|
|
c = c || per_cpu(rcu_preempt_data, cpu).nxtlist;
|
|
}
|
|
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
|
|
rcu_sched_qs(cpu);
|
|
force_quiescent_state(&rcu_sched_state, 0);
|
|
c = c || per_cpu(rcu_sched_data, cpu).nxtlist;
|
|
}
|
|
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
|
|
rcu_bh_qs(cpu);
|
|
force_quiescent_state(&rcu_bh_state, 0);
|
|
c = c || per_cpu(rcu_bh_data, cpu).nxtlist;
|
|
}
|
|
|
|
/*
|
|
* If RCU callbacks are still pending, RCU still needs this CPU.
|
|
* So try forcing the callbacks through the grace period.
|
|
*/
|
|
if (c) {
|
|
trace_rcu_prep_idle("More callbacks");
|
|
invoke_rcu_core();
|
|
} else
|
|
trace_rcu_prep_idle("Callbacks drained");
|
|
}
|
|
|
|
/*
|
|
* Wake up a CPU by invoking the RCU core. Intended for use by
|
|
* rcu_wake_cpus_for_gp_end(), which passes this function to
|
|
* smp_call_function_single().
|
|
*/
|
|
static void rcu_wake_cpu(void *unused)
|
|
{
|
|
trace_rcu_prep_idle("CPU awakened at GP end");
|
|
invoke_rcu_core();
|
|
}
|
|
|
|
/*
|
|
* If an RCU grace period ended recently, scan the rcu_awake_at_gp_end
|
|
* per-CPU variables, and wake up any CPUs that requested a wakeup.
|
|
*/
|
|
static void rcu_wake_cpus_for_gp_end(void)
|
|
{
|
|
int cpu;
|
|
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
|
|
|
|
if (!rdtp->wake_gp_end)
|
|
return;
|
|
rdtp->wake_gp_end = 0;
|
|
for_each_online_cpu(cpu) {
|
|
if (per_cpu(rcu_awake_at_gp_end, cpu)) {
|
|
per_cpu(rcu_awake_at_gp_end, cpu) = 0;
|
|
smp_call_function_single(cpu, rcu_wake_cpu, NULL, 0);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* A grace period has just ended, and so we will need to awaken CPUs
|
|
* that now have work to do. But we cannot send IPIs with interrupts
|
|
* disabled, so just set a flag so that this will happen upon exit
|
|
* from RCU core processing.
|
|
*/
|
|
static void rcu_schedule_wake_gp_end(void)
|
|
{
|
|
struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
|
|
|
|
rdtp->wake_gp_end = 1;
|
|
}
|
|
|
|
/* @@@ need tracing as well. */
|
|
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|