sched: Fix rq->nr_uninterruptible update race (4ca9b72b) · Commits · 戴 / test

KOSAKI Motohiro noticed the following race: > CPU0 CPU1 > -------------------------------------------------------- > deactivate_task() > task->state = TASK_UNINTERRUPTIBLE; > activate_task() > rq->nr_uninterruptible--; > > schedule() > deactivate_task() > rq->nr_uninterruptible++; > Kosaki-San's scenario is possible when CPU0 runs __sched_setscheduler() against CPU1's current @task. __sched_setscheduler() does a dequeue/enqueue in order to move the task to its new queue (position) to reflect the newly provided scheduling parameters. However it should be completely invariant to nr_uninterruptible accounting, sched_setscheduler() doesn't affect readyness to run, merely policy on when to run. So convert the inappropriate activate/deactivate_task usage to enqueue/dequeue_task, which avoids the nr_uninterruptible accounting. Also convert the two other sites: __migrate_task() and normalize_task() that still use activate/deactivate_task. These sites aren't really a problem since __migrate_task() will only be called on non-running task (and therefore are immume to the described problem) and normalize_task() isn't ever used on regular systems. Also remove the comments from activate/deactivate_task since they're misleading at best. Reported-by:

KOSAKI Motohiro <kosaki.motohiro@gmail.com> Signed-off-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1327486224.2614.45.camel@laptop Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/sched/core.c

+6 −12

Original line number	Diff line number	Diff line
		@@ -723,9 +723,6 @@ static void dequeue_task(struct rq rq, struct task_struct p, int flags)
		p->sched_class->dequeue_task(rq, p, flags);
		}

		/*
		* activate_task - move a task to the runqueue.
		*/
		void activate_task(struct rq rq, struct task_struct p, int flags)
		{
		if (task_contributes_to_load(p))
		@@ -734,9 +731,6 @@ void activate_task(struct rq rq, struct task_struct p, int flags)
		enqueue_task(rq, p, flags);
		}

		/*
		* deactivate_task - remove a task from the runqueue.
		*/
		void deactivate_task(struct rq rq, struct task_struct p, int flags)
		{
		if (task_contributes_to_load(p))
		@@ -4134,7 +4128,7 @@ recheck:
		on_rq = p->on_rq;
		running = task_current(rq, p);
		if (on_rq)
		deactivate_task(rq, p, 0);
		dequeue_task(rq, p, 0);
		if (running)
		p->sched_class->put_prev_task(rq, p);

		@@ -4147,7 +4141,7 @@ recheck:
		if (running)
		p->sched_class->set_curr_task(rq);
		if (on_rq)
		activate_task(rq, p, 0);
		enqueue_task(rq, p, 0);

		check_class_changed(rq, p, prev_class, oldprio);
		task_rq_unlock(rq, p, &flags);
		@@ -4998,9 +4992,9 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
		* placed properly.
		*/
		if (p->on_rq) {
		deactivate_task(rq_src, p, 0);
		dequeue_task(rq_src, p, 0);
		set_task_cpu(p, dest_cpu);
		activate_task(rq_dest, p, 0);
		enqueue_task(rq_dest, p, 0);
		check_preempt_curr(rq_dest, p, 0);
		}
		done:
		@@ -7032,10 +7026,10 @@ static void normalize_task(struct rq rq, struct task_struct p)

		on_rq = p->on_rq;
		if (on_rq)
		deactivate_task(rq, p, 0);
		dequeue_task(rq, p, 0);
		__setscheduler(rq, p, SCHED_NORMAL, 0);
		if (on_rq) {
		activate_task(rq, p, 0);
		enqueue_task(rq, p, 0);
		resched_task(rq->curr);
		}

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