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![Paul E. McKenney](/assets/img/avatar_default.png)
The current implementation of RCU_FAST_NO_HZ prevents CPUs from entering dyntick-idle state if they have RCU callbacks pending. Unfortunately, this has the side-effect of often preventing them from entering this state, especially if at least one other CPU is not in dyntick-idle state. However, the resulting per-tick wakeup is wasteful in many cases: if the CPU has already fully responded to the current RCU grace period, there will be nothing for it to do until this grace period ends, which will frequently take several jiffies. This commit therefore permits a CPU that has done everything that the current grace period has asked of it (rcu_pending() == 0) even if it still as RCU callbacks pending. However, such a CPU posts a timer to wake it up several jiffies later (6 jiffies, based on experience with grace-period lengths). This wakeup is required to handle situations that can result in all CPUs being in dyntick-idle mode, thus failing to ever complete the current grace period. If a CPU wakes up before the timer goes off, then it cancels that timer, thus avoiding spurious wakeups. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2157 lines
63 KiB
C
2157 lines
63 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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}
|
|
#endif /* #ifdef CONFIG_PROVE_LOCKING */
|
|
}
|
|
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
|
|
|
|
#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period on the specified rcu_node structure.
|
|
*/
|
|
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
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 not have RCU_FAST_NO_HZ, just check whether this CPU needs
|
|
* any flavor of RCU.
|
|
*/
|
|
int rcu_needs_cpu(int cpu)
|
|
{
|
|
return rcu_cpu_has_callbacks(cpu);
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
|
|
*/
|
|
static void rcu_prepare_for_idle_init(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
|
|
* after it.
|
|
*/
|
|
static void rcu_cleanup_after_idle(int 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)
|
|
{
|
|
}
|
|
|
|
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
#define RCU_NEEDS_CPU_FLUSHES 5 /* Allow for callback self-repost. */
|
|
#define RCU_IDLE_GP_DELAY 6 /* Roughly one grace period. */
|
|
static DEFINE_PER_CPU(int, rcu_dyntick_drain);
|
|
static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
|
|
static DEFINE_PER_CPU(struct hrtimer, rcu_idle_gp_timer);
|
|
static ktime_t rcu_idle_gp_wait;
|
|
|
|
/*
|
|
* 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;
|
|
}
|
|
|
|
/*
|
|
* Timer handler used to force CPU to start pushing its remaining RCU
|
|
* callbacks in the case where it entered dyntick-idle mode with callbacks
|
|
* pending. The hander doesn't really need to do anything because the
|
|
* real work is done upon re-entry to idle, or by the next scheduling-clock
|
|
* interrupt should idle not be re-entered.
|
|
*/
|
|
static enum hrtimer_restart rcu_idle_gp_timer_func(struct hrtimer *hrtp)
|
|
{
|
|
trace_rcu_prep_idle("Timer");
|
|
return HRTIMER_NORESTART;
|
|
}
|
|
|
|
/*
|
|
* Initialize the timer used to pull CPUs out of dyntick-idle mode.
|
|
*/
|
|
static void rcu_prepare_for_idle_init(int cpu)
|
|
{
|
|
static int firsttime = 1;
|
|
struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu);
|
|
|
|
hrtimer_init(hrtp, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
|
|
hrtp->function = rcu_idle_gp_timer_func;
|
|
if (firsttime) {
|
|
unsigned int upj = jiffies_to_usecs(RCU_IDLE_GP_DELAY);
|
|
|
|
rcu_idle_gp_wait = ns_to_ktime(upj * (u64)1000);
|
|
firsttime = 0;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clean up for exit from idle. Because we are exiting from idle, there
|
|
* is no longer any point to rcu_idle_gp_timer, so cancel it. This will
|
|
* do nothing if this timer is not active, so just cancel it unconditionally.
|
|
*/
|
|
static void rcu_cleanup_after_idle(int cpu)
|
|
{
|
|
hrtimer_cancel(&per_cpu(rcu_idle_gp_timer, cpu));
|
|
}
|
|
|
|
/*
|
|
* 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)
|
|
{
|
|
unsigned long flags;
|
|
|
|
local_irq_save(flags);
|
|
|
|
/*
|
|
* If there are no callbacks on this CPU, enter dyntick-idle mode.
|
|
* Also reset state to avoid prejudicing later attempts.
|
|
*/
|
|
if (!rcu_cpu_has_callbacks(cpu)) {
|
|
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
|
|
per_cpu(rcu_dyntick_drain, cpu) = 0;
|
|
local_irq_restore(flags);
|
|
trace_rcu_prep_idle("No callbacks");
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If in holdoff mode, just return. We will presumably have
|
|
* refrained from disabling the scheduling-clock tick.
|
|
*/
|
|
if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) {
|
|
local_irq_restore(flags);
|
|
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) {
|
|
/* Can we go dyntick-idle despite still having callbacks? */
|
|
if (!rcu_pending(cpu)) {
|
|
trace_rcu_prep_idle("Dyntick with callbacks");
|
|
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
|
|
hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
|
|
rcu_idle_gp_wait, HRTIMER_MODE_REL);
|
|
return; /* Nothing more to do immediately. */
|
|
}
|
|
|
|
/* We have hit the limit, so time to give up. */
|
|
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
|
|
local_irq_restore(flags);
|
|
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) {
|
|
local_irq_restore(flags);
|
|
rcu_preempt_qs(cpu);
|
|
force_quiescent_state(&rcu_preempt_state, 0);
|
|
local_irq_save(flags);
|
|
}
|
|
#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
|
|
local_irq_restore(flags);
|
|
rcu_sched_qs(cpu);
|
|
force_quiescent_state(&rcu_sched_state, 0);
|
|
local_irq_save(flags);
|
|
}
|
|
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
|
|
local_irq_restore(flags);
|
|
rcu_bh_qs(cpu);
|
|
force_quiescent_state(&rcu_bh_state, 0);
|
|
local_irq_save(flags);
|
|
}
|
|
|
|
/*
|
|
* If RCU callbacks are still pending, RCU still needs this CPU.
|
|
* So try forcing the callbacks through the grace period.
|
|
*/
|
|
if (rcu_cpu_has_callbacks(cpu)) {
|
|
local_irq_restore(flags);
|
|
trace_rcu_prep_idle("More callbacks");
|
|
invoke_rcu_core();
|
|
} else {
|
|
local_irq_restore(flags);
|
|
trace_rcu_prep_idle("Callbacks drained");
|
|
}
|
|
}
|
|
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|