rcu-tasks: Move Tasks RCU to its own file
This code-movement-only commit is in preparation for adding an additional flavor of Tasks RCU, which relies on workqueues to detect grace periods. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney
parent
5bef8da66a
commit
eacd6f04a1
370
kernel/rcu/tasks.h
Normal file
370
kernel/rcu/tasks.h
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@ -0,0 +1,370 @@
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/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Task-based RCU implementations.
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*
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* Copyright (C) 2020 Paul E. McKenney
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*/
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#ifdef CONFIG_TASKS_RCU
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/*
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* Simple variant of RCU whose quiescent states are voluntary context
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* switch, cond_resched_rcu_qs(), user-space execution, and idle.
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* As such, grace periods can take one good long time. There are no
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* read-side primitives similar to rcu_read_lock() and rcu_read_unlock()
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* because this implementation is intended to get the system into a safe
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* state for some of the manipulations involved in tracing and the like.
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* Finally, this implementation does not support high call_rcu_tasks()
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* rates from multiple CPUs. If this is required, per-CPU callback lists
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* will be needed.
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*/
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/* Global list of callbacks and associated lock. */
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static struct rcu_head *rcu_tasks_cbs_head;
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static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
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static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
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static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
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/* Track exiting tasks in order to allow them to be waited for. */
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DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
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/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
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#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
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static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
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module_param(rcu_task_stall_timeout, int, 0644);
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static struct task_struct *rcu_tasks_kthread_ptr;
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/**
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* call_rcu_tasks() - Queue an RCU for invocation task-based grace period
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* @rhp: structure to be used for queueing the RCU updates.
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* @func: actual callback function to be invoked after the grace period
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*
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* The callback function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. call_rcu_tasks() assumes
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* that the read-side critical sections end at a voluntary context
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* switch (not a preemption!), cond_resched_rcu_qs(), entry into idle,
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* or transition to usermode execution. As such, there are no read-side
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* primitives analogous to rcu_read_lock() and rcu_read_unlock() because
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* this primitive is intended to determine that all tasks have passed
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* through a safe state, not so much for data-strcuture synchronization.
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*
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* See the description of call_rcu() for more detailed information on
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* memory ordering guarantees.
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*/
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void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
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{
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unsigned long flags;
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bool needwake;
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rhp->next = NULL;
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rhp->func = func;
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raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
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needwake = !rcu_tasks_cbs_head;
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WRITE_ONCE(*rcu_tasks_cbs_tail, rhp);
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rcu_tasks_cbs_tail = &rhp->next;
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raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
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/* We can't create the thread unless interrupts are enabled. */
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if (needwake && READ_ONCE(rcu_tasks_kthread_ptr))
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wake_up(&rcu_tasks_cbs_wq);
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}
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EXPORT_SYMBOL_GPL(call_rcu_tasks);
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/**
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* synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
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*
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* Control will return to the caller some time after a full rcu-tasks
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* grace period has elapsed, in other words after all currently
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* executing rcu-tasks read-side critical sections have elapsed. These
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* read-side critical sections are delimited by calls to schedule(),
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* cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
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* to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
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*
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* This is a very specialized primitive, intended only for a few uses in
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* tracing and other situations requiring manipulation of function
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* preambles and profiling hooks. The synchronize_rcu_tasks() function
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* is not (yet) intended for heavy use from multiple CPUs.
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*
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* Note that this guarantee implies further memory-ordering guarantees.
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* On systems with more than one CPU, when synchronize_rcu_tasks() returns,
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* each CPU is guaranteed to have executed a full memory barrier since the
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* end of its last RCU-tasks read-side critical section whose beginning
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* preceded the call to synchronize_rcu_tasks(). In addition, each CPU
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* having an RCU-tasks read-side critical section that extends beyond
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* the return from synchronize_rcu_tasks() is guaranteed to have executed
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* a full memory barrier after the beginning of synchronize_rcu_tasks()
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* and before the beginning of that RCU-tasks read-side critical section.
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* Note that these guarantees include CPUs that are offline, idle, or
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* executing in user mode, as well as CPUs that are executing in the kernel.
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*
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* Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
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* to its caller on CPU B, then both CPU A and CPU B are guaranteed
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* to have executed a full memory barrier during the execution of
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* synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
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* (but again only if the system has more than one CPU).
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*/
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void synchronize_rcu_tasks(void)
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{
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/* Complain if the scheduler has not started. */
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RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
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"synchronize_rcu_tasks called too soon");
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/* Wait for the grace period. */
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wait_rcu_gp(call_rcu_tasks);
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}
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EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
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/**
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* rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
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*
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* Although the current implementation is guaranteed to wait, it is not
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* obligated to, for example, if there are no pending callbacks.
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*/
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void rcu_barrier_tasks(void)
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{
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/* There is only one callback queue, so this is easy. ;-) */
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synchronize_rcu_tasks();
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}
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EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
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/* See if tasks are still holding out, complain if so. */
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static void check_holdout_task(struct task_struct *t,
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bool needreport, bool *firstreport)
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{
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int cpu;
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if (!READ_ONCE(t->rcu_tasks_holdout) ||
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t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
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!READ_ONCE(t->on_rq) ||
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(IS_ENABLED(CONFIG_NO_HZ_FULL) &&
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!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
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WRITE_ONCE(t->rcu_tasks_holdout, false);
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list_del_init(&t->rcu_tasks_holdout_list);
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put_task_struct(t);
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return;
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}
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rcu_request_urgent_qs_task(t);
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if (!needreport)
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return;
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if (*firstreport) {
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pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
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*firstreport = false;
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}
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cpu = task_cpu(t);
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pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
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t, ".I"[is_idle_task(t)],
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"N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
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t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
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t->rcu_tasks_idle_cpu, cpu);
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sched_show_task(t);
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}
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/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
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static int __noreturn rcu_tasks_kthread(void *arg)
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{
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unsigned long flags;
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struct task_struct *g, *t;
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unsigned long lastreport;
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struct rcu_head *list;
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struct rcu_head *next;
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LIST_HEAD(rcu_tasks_holdouts);
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int fract;
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/* Run on housekeeping CPUs by default. Sysadm can move if desired. */
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housekeeping_affine(current, HK_FLAG_RCU);
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/*
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* Each pass through the following loop makes one check for
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* newly arrived callbacks, and, if there are some, waits for
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* one RCU-tasks grace period and then invokes the callbacks.
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* This loop is terminated by the system going down. ;-)
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*/
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for (;;) {
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/* Pick up any new callbacks. */
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raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
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list = rcu_tasks_cbs_head;
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rcu_tasks_cbs_head = NULL;
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rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
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raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
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/* If there were none, wait a bit and start over. */
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if (!list) {
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wait_event_interruptible(rcu_tasks_cbs_wq,
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READ_ONCE(rcu_tasks_cbs_head));
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if (!rcu_tasks_cbs_head) {
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WARN_ON(signal_pending(current));
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schedule_timeout_interruptible(HZ/10);
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}
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continue;
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}
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/*
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* Wait for all pre-existing t->on_rq and t->nvcsw
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* transitions to complete. Invoking synchronize_rcu()
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* suffices because all these transitions occur with
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* interrupts disabled. Without this synchronize_rcu(),
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* a read-side critical section that started before the
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* grace period might be incorrectly seen as having started
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* after the grace period.
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*
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* This synchronize_rcu() also dispenses with the
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* need for a memory barrier on the first store to
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* ->rcu_tasks_holdout, as it forces the store to happen
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* after the beginning of the grace period.
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*/
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synchronize_rcu();
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/*
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* There were callbacks, so we need to wait for an
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* RCU-tasks grace period. Start off by scanning
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* the task list for tasks that are not already
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* voluntarily blocked. Mark these tasks and make
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* a list of them in rcu_tasks_holdouts.
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*/
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rcu_read_lock();
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for_each_process_thread(g, t) {
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if (t != current && READ_ONCE(t->on_rq) &&
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!is_idle_task(t)) {
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get_task_struct(t);
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t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
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WRITE_ONCE(t->rcu_tasks_holdout, true);
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list_add(&t->rcu_tasks_holdout_list,
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&rcu_tasks_holdouts);
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}
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}
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rcu_read_unlock();
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/*
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* Wait for tasks that are in the process of exiting.
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* This does only part of the job, ensuring that all
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* tasks that were previously exiting reach the point
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* where they have disabled preemption, allowing the
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* later synchronize_rcu() to finish the job.
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*/
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synchronize_srcu(&tasks_rcu_exit_srcu);
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/*
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* Each pass through the following loop scans the list
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* of holdout tasks, removing any that are no longer
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* holdouts. When the list is empty, we are done.
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*/
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lastreport = jiffies;
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/* Start off with HZ/10 wait and slowly back off to 1 HZ wait*/
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fract = 10;
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for (;;) {
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bool firstreport;
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bool needreport;
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int rtst;
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struct task_struct *t1;
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if (list_empty(&rcu_tasks_holdouts))
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break;
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/* Slowly back off waiting for holdouts */
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schedule_timeout_interruptible(HZ/fract);
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if (fract > 1)
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fract--;
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rtst = READ_ONCE(rcu_task_stall_timeout);
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needreport = rtst > 0 &&
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time_after(jiffies, lastreport + rtst);
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if (needreport)
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lastreport = jiffies;
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firstreport = true;
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WARN_ON(signal_pending(current));
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list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
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rcu_tasks_holdout_list) {
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check_holdout_task(t, needreport, &firstreport);
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cond_resched();
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}
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}
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/*
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* Because ->on_rq and ->nvcsw are not guaranteed
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* to have a full memory barriers prior to them in the
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* schedule() path, memory reordering on other CPUs could
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* cause their RCU-tasks read-side critical sections to
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* extend past the end of the grace period. However,
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* because these ->nvcsw updates are carried out with
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* interrupts disabled, we can use synchronize_rcu()
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* to force the needed ordering on all such CPUs.
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*
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* This synchronize_rcu() also confines all
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* ->rcu_tasks_holdout accesses to be within the grace
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* period, avoiding the need for memory barriers for
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* ->rcu_tasks_holdout accesses.
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*
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* In addition, this synchronize_rcu() waits for exiting
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* tasks to complete their final preempt_disable() region
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* of execution, cleaning up after the synchronize_srcu()
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* above.
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*/
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synchronize_rcu();
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/* Invoke the callbacks. */
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while (list) {
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next = list->next;
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local_bh_disable();
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list->func(list);
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local_bh_enable();
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list = next;
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cond_resched();
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}
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/* Paranoid sleep to keep this from entering a tight loop */
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schedule_timeout_uninterruptible(HZ/10);
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}
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}
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/* Spawn rcu_tasks_kthread() at core_initcall() time. */
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static int __init rcu_spawn_tasks_kthread(void)
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{
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struct task_struct *t;
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t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
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if (WARN_ONCE(IS_ERR(t), "%s: Could not start Tasks-RCU grace-period kthread, OOM is now expected behavior\n", __func__))
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return 0;
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smp_mb(); /* Ensure others see full kthread. */
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WRITE_ONCE(rcu_tasks_kthread_ptr, t);
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return 0;
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}
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core_initcall(rcu_spawn_tasks_kthread);
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/* Do the srcu_read_lock() for the above synchronize_srcu(). */
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void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
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{
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preempt_disable();
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current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
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preempt_enable();
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}
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/* Do the srcu_read_unlock() for the above synchronize_srcu(). */
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void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
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{
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preempt_disable();
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__srcu_read_unlock(&tasks_rcu_exit_srcu, current->rcu_tasks_idx);
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preempt_enable();
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}
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#endif /* #ifdef CONFIG_TASKS_RCU */
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#ifndef CONFIG_TINY_RCU
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/*
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* Print any non-default Tasks RCU settings.
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*/
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static void __init rcu_tasks_bootup_oddness(void)
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{
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#ifdef CONFIG_TASKS_RCU
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if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
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pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
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else
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pr_info("\tTasks RCU enabled.\n");
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#endif /* #ifdef CONFIG_TASKS_RCU */
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}
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#endif /* #ifndef CONFIG_TINY_RCU */
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@ -514,370 +514,6 @@ int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls.
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EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_at_boot);
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module_param(rcu_cpu_stall_suppress_at_boot, int, 0444);
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#ifdef CONFIG_TASKS_RCU
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/*
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* Simple variant of RCU whose quiescent states are voluntary context
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* switch, cond_resched_rcu_qs(), user-space execution, and idle.
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* As such, grace periods can take one good long time. There are no
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* read-side primitives similar to rcu_read_lock() and rcu_read_unlock()
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* because this implementation is intended to get the system into a safe
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* state for some of the manipulations involved in tracing and the like.
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* Finally, this implementation does not support high call_rcu_tasks()
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* rates from multiple CPUs. If this is required, per-CPU callback lists
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* will be needed.
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*/
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/* Global list of callbacks and associated lock. */
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static struct rcu_head *rcu_tasks_cbs_head;
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static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
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static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
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static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
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/* Track exiting tasks in order to allow them to be waited for. */
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DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
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/* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
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#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
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static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
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module_param(rcu_task_stall_timeout, int, 0644);
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static struct task_struct *rcu_tasks_kthread_ptr;
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|
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/**
|
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* call_rcu_tasks() - Queue an RCU for invocation task-based grace period
|
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* @rhp: structure to be used for queueing the RCU updates.
|
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* @func: actual callback function to be invoked after the grace period
|
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*
|
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* The callback function will be invoked some time after a full grace
|
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* period elapses, in other words after all currently executing RCU
|
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* read-side critical sections have completed. call_rcu_tasks() assumes
|
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* that the read-side critical sections end at a voluntary context
|
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* switch (not a preemption!), cond_resched_rcu_qs(), entry into idle,
|
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* or transition to usermode execution. As such, there are no read-side
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* primitives analogous to rcu_read_lock() and rcu_read_unlock() because
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||||
* this primitive is intended to determine that all tasks have passed
|
||||
* through a safe state, not so much for data-strcuture synchronization.
|
||||
*
|
||||
* See the description of call_rcu() for more detailed information on
|
||||
* memory ordering guarantees.
|
||||
*/
|
||||
void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
|
||||
{
|
||||
unsigned long flags;
|
||||
bool needwake;
|
||||
|
||||
rhp->next = NULL;
|
||||
rhp->func = func;
|
||||
raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
|
||||
needwake = !rcu_tasks_cbs_head;
|
||||
WRITE_ONCE(*rcu_tasks_cbs_tail, rhp);
|
||||
rcu_tasks_cbs_tail = &rhp->next;
|
||||
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
|
||||
/* We can't create the thread unless interrupts are enabled. */
|
||||
if (needwake && READ_ONCE(rcu_tasks_kthread_ptr))
|
||||
wake_up(&rcu_tasks_cbs_wq);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(call_rcu_tasks);
|
||||
|
||||
/**
|
||||
* synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
|
||||
*
|
||||
* Control will return to the caller some time after a full rcu-tasks
|
||||
* grace period has elapsed, in other words after all currently
|
||||
* executing rcu-tasks read-side critical sections have elapsed. These
|
||||
* read-side critical sections are delimited by calls to schedule(),
|
||||
* cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
|
||||
* to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
|
||||
*
|
||||
* This is a very specialized primitive, intended only for a few uses in
|
||||
* tracing and other situations requiring manipulation of function
|
||||
* preambles and profiling hooks. The synchronize_rcu_tasks() function
|
||||
* is not (yet) intended for heavy use from multiple CPUs.
|
||||
*
|
||||
* Note that this guarantee implies further memory-ordering guarantees.
|
||||
* On systems with more than one CPU, when synchronize_rcu_tasks() returns,
|
||||
* each CPU is guaranteed to have executed a full memory barrier since the
|
||||
* end of its last RCU-tasks read-side critical section whose beginning
|
||||
* preceded the call to synchronize_rcu_tasks(). In addition, each CPU
|
||||
* having an RCU-tasks read-side critical section that extends beyond
|
||||
* the return from synchronize_rcu_tasks() is guaranteed to have executed
|
||||
* a full memory barrier after the beginning of synchronize_rcu_tasks()
|
||||
* and before the beginning of that RCU-tasks read-side critical section.
|
||||
* Note that these guarantees include CPUs that are offline, idle, or
|
||||
* executing in user mode, as well as CPUs that are executing in the kernel.
|
||||
*
|
||||
* Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
|
||||
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
|
||||
* to have executed a full memory barrier during the execution of
|
||||
* synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
|
||||
* (but again only if the system has more than one CPU).
|
||||
*/
|
||||
void synchronize_rcu_tasks(void)
|
||||
{
|
||||
/* Complain if the scheduler has not started. */
|
||||
RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
|
||||
"synchronize_rcu_tasks called too soon");
|
||||
|
||||
/* Wait for the grace period. */
|
||||
wait_rcu_gp(call_rcu_tasks);
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
|
||||
|
||||
/**
|
||||
* rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
|
||||
*
|
||||
* Although the current implementation is guaranteed to wait, it is not
|
||||
* obligated to, for example, if there are no pending callbacks.
|
||||
*/
|
||||
void rcu_barrier_tasks(void)
|
||||
{
|
||||
/* There is only one callback queue, so this is easy. ;-) */
|
||||
synchronize_rcu_tasks();
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
|
||||
|
||||
/* See if tasks are still holding out, complain if so. */
|
||||
static void check_holdout_task(struct task_struct *t,
|
||||
bool needreport, bool *firstreport)
|
||||
{
|
||||
int cpu;
|
||||
|
||||
if (!READ_ONCE(t->rcu_tasks_holdout) ||
|
||||
t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
|
||||
!READ_ONCE(t->on_rq) ||
|
||||
(IS_ENABLED(CONFIG_NO_HZ_FULL) &&
|
||||
!is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
|
||||
WRITE_ONCE(t->rcu_tasks_holdout, false);
|
||||
list_del_init(&t->rcu_tasks_holdout_list);
|
||||
put_task_struct(t);
|
||||
return;
|
||||
}
|
||||
rcu_request_urgent_qs_task(t);
|
||||
if (!needreport)
|
||||
return;
|
||||
if (*firstreport) {
|
||||
pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
|
||||
*firstreport = false;
|
||||
}
|
||||
cpu = task_cpu(t);
|
||||
pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
|
||||
t, ".I"[is_idle_task(t)],
|
||||
"N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
|
||||
t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
|
||||
t->rcu_tasks_idle_cpu, cpu);
|
||||
sched_show_task(t);
|
||||
}
|
||||
|
||||
/* RCU-tasks kthread that detects grace periods and invokes callbacks. */
|
||||
static int __noreturn rcu_tasks_kthread(void *arg)
|
||||
{
|
||||
unsigned long flags;
|
||||
struct task_struct *g, *t;
|
||||
unsigned long lastreport;
|
||||
struct rcu_head *list;
|
||||
struct rcu_head *next;
|
||||
LIST_HEAD(rcu_tasks_holdouts);
|
||||
int fract;
|
||||
|
||||
/* Run on housekeeping CPUs by default. Sysadm can move if desired. */
|
||||
housekeeping_affine(current, HK_FLAG_RCU);
|
||||
|
||||
/*
|
||||
* Each pass through the following loop makes one check for
|
||||
* newly arrived callbacks, and, if there are some, waits for
|
||||
* one RCU-tasks grace period and then invokes the callbacks.
|
||||
* This loop is terminated by the system going down. ;-)
|
||||
*/
|
||||
for (;;) {
|
||||
|
||||
/* Pick up any new callbacks. */
|
||||
raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
|
||||
list = rcu_tasks_cbs_head;
|
||||
rcu_tasks_cbs_head = NULL;
|
||||
rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
|
||||
raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
|
||||
|
||||
/* If there were none, wait a bit and start over. */
|
||||
if (!list) {
|
||||
wait_event_interruptible(rcu_tasks_cbs_wq,
|
||||
READ_ONCE(rcu_tasks_cbs_head));
|
||||
if (!rcu_tasks_cbs_head) {
|
||||
WARN_ON(signal_pending(current));
|
||||
schedule_timeout_interruptible(HZ/10);
|
||||
}
|
||||
continue;
|
||||
}
|
||||
|
||||
/*
|
||||
* Wait for all pre-existing t->on_rq and t->nvcsw
|
||||
* transitions to complete. Invoking synchronize_rcu()
|
||||
* suffices because all these transitions occur with
|
||||
* interrupts disabled. Without this synchronize_rcu(),
|
||||
* a read-side critical section that started before the
|
||||
* grace period might be incorrectly seen as having started
|
||||
* after the grace period.
|
||||
*
|
||||
* This synchronize_rcu() also dispenses with the
|
||||
* need for a memory barrier on the first store to
|
||||
* ->rcu_tasks_holdout, as it forces the store to happen
|
||||
* after the beginning of the grace period.
|
||||
*/
|
||||
synchronize_rcu();
|
||||
|
||||
/*
|
||||
* There were callbacks, so we need to wait for an
|
||||
* RCU-tasks grace period. Start off by scanning
|
||||
* the task list for tasks that are not already
|
||||
* voluntarily blocked. Mark these tasks and make
|
||||
* a list of them in rcu_tasks_holdouts.
|
||||
*/
|
||||
rcu_read_lock();
|
||||
for_each_process_thread(g, t) {
|
||||
if (t != current && READ_ONCE(t->on_rq) &&
|
||||
!is_idle_task(t)) {
|
||||
get_task_struct(t);
|
||||
t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
|
||||
WRITE_ONCE(t->rcu_tasks_holdout, true);
|
||||
list_add(&t->rcu_tasks_holdout_list,
|
||||
&rcu_tasks_holdouts);
|
||||
}
|
||||
}
|
||||
rcu_read_unlock();
|
||||
|
||||
/*
|
||||
* Wait for tasks that are in the process of exiting.
|
||||
* This does only part of the job, ensuring that all
|
||||
* tasks that were previously exiting reach the point
|
||||
* where they have disabled preemption, allowing the
|
||||
* later synchronize_rcu() to finish the job.
|
||||
*/
|
||||
synchronize_srcu(&tasks_rcu_exit_srcu);
|
||||
|
||||
/*
|
||||
* Each pass through the following loop scans the list
|
||||
* of holdout tasks, removing any that are no longer
|
||||
* holdouts. When the list is empty, we are done.
|
||||
*/
|
||||
lastreport = jiffies;
|
||||
|
||||
/* Start off with HZ/10 wait and slowly back off to 1 HZ wait*/
|
||||
fract = 10;
|
||||
|
||||
for (;;) {
|
||||
bool firstreport;
|
||||
bool needreport;
|
||||
int rtst;
|
||||
struct task_struct *t1;
|
||||
|
||||
if (list_empty(&rcu_tasks_holdouts))
|
||||
break;
|
||||
|
||||
/* Slowly back off waiting for holdouts */
|
||||
schedule_timeout_interruptible(HZ/fract);
|
||||
|
||||
if (fract > 1)
|
||||
fract--;
|
||||
|
||||
rtst = READ_ONCE(rcu_task_stall_timeout);
|
||||
needreport = rtst > 0 &&
|
||||
time_after(jiffies, lastreport + rtst);
|
||||
if (needreport)
|
||||
lastreport = jiffies;
|
||||
firstreport = true;
|
||||
WARN_ON(signal_pending(current));
|
||||
list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
|
||||
rcu_tasks_holdout_list) {
|
||||
check_holdout_task(t, needreport, &firstreport);
|
||||
cond_resched();
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
* Because ->on_rq and ->nvcsw are not guaranteed
|
||||
* to have a full memory barriers prior to them in the
|
||||
* schedule() path, memory reordering on other CPUs could
|
||||
* cause their RCU-tasks read-side critical sections to
|
||||
* extend past the end of the grace period. However,
|
||||
* because these ->nvcsw updates are carried out with
|
||||
* interrupts disabled, we can use synchronize_rcu()
|
||||
* to force the needed ordering on all such CPUs.
|
||||
*
|
||||
* This synchronize_rcu() also confines all
|
||||
* ->rcu_tasks_holdout accesses to be within the grace
|
||||
* period, avoiding the need for memory barriers for
|
||||
* ->rcu_tasks_holdout accesses.
|
||||
*
|
||||
* In addition, this synchronize_rcu() waits for exiting
|
||||
* tasks to complete their final preempt_disable() region
|
||||
* of execution, cleaning up after the synchronize_srcu()
|
||||
* above.
|
||||
*/
|
||||
synchronize_rcu();
|
||||
|
||||
/* Invoke the callbacks. */
|
||||
while (list) {
|
||||
next = list->next;
|
||||
local_bh_disable();
|
||||
list->func(list);
|
||||
local_bh_enable();
|
||||
list = next;
|
||||
cond_resched();
|
||||
}
|
||||
/* Paranoid sleep to keep this from entering a tight loop */
|
||||
schedule_timeout_uninterruptible(HZ/10);
|
||||
}
|
||||
}
|
||||
|
||||
/* Spawn rcu_tasks_kthread() at core_initcall() time. */
|
||||
static int __init rcu_spawn_tasks_kthread(void)
|
||||
{
|
||||
struct task_struct *t;
|
||||
|
||||
t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
|
||||
if (WARN_ONCE(IS_ERR(t), "%s: Could not start Tasks-RCU grace-period kthread, OOM is now expected behavior\n", __func__))
|
||||
return 0;
|
||||
smp_mb(); /* Ensure others see full kthread. */
|
||||
WRITE_ONCE(rcu_tasks_kthread_ptr, t);
|
||||
return 0;
|
||||
}
|
||||
core_initcall(rcu_spawn_tasks_kthread);
|
||||
|
||||
/* Do the srcu_read_lock() for the above synchronize_srcu(). */
|
||||
void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
|
||||
{
|
||||
preempt_disable();
|
||||
current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
|
||||
preempt_enable();
|
||||
}
|
||||
|
||||
/* Do the srcu_read_unlock() for the above synchronize_srcu(). */
|
||||
void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
|
||||
{
|
||||
preempt_disable();
|
||||
__srcu_read_unlock(&tasks_rcu_exit_srcu, current->rcu_tasks_idx);
|
||||
preempt_enable();
|
||||
}
|
||||
|
||||
#endif /* #ifdef CONFIG_TASKS_RCU */
|
||||
|
||||
#ifndef CONFIG_TINY_RCU
|
||||
|
||||
/*
|
||||
* Print any non-default Tasks RCU settings.
|
||||
*/
|
||||
static void __init rcu_tasks_bootup_oddness(void)
|
||||
{
|
||||
#ifdef CONFIG_TASKS_RCU
|
||||
if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
|
||||
pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
|
||||
else
|
||||
pr_info("\tTasks RCU enabled.\n");
|
||||
#endif /* #ifdef CONFIG_TASKS_RCU */
|
||||
}
|
||||
|
||||
#endif /* #ifndef CONFIG_TINY_RCU */
|
||||
|
||||
#ifdef CONFIG_PROVE_RCU
|
||||
|
||||
/*
|
||||
|
|
@ -948,6 +584,8 @@ late_initcall(rcu_verify_early_boot_tests);
|
|||
void rcu_early_boot_tests(void) {}
|
||||
#endif /* CONFIG_PROVE_RCU */
|
||||
|
||||
#include "tasks.h"
|
||||
|
||||
#ifndef CONFIG_TINY_RCU
|
||||
|
||||
/*
|
||||
|
|
|
|||
Loading…
Reference in a new issue