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Commit 094f4691 authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Ingo Molnar
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sched/fair: Initialize throttle_count for new task-groups lazily 



Cgroup created inside throttled group must inherit current throttle_count.
Broken throttle_count allows to nominate throttled entries as a next buddy,
later this leads to null pointer dereference in pick_next_task_fair().

This patch initialize cfs_rq->throttle_count at first enqueue: laziness
allows to skip locking all rq at group creation. Lazy approach also allows
to skip full sub-tree scan at throttling hierarchy (not in this patch).

Signed-off-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bsegall@google.com
Link: http://lkml.kernel.org/r/146608182119.21870.8439834428248129633.stgit@buzz


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 89741892

kernel/sched/fair.c

+20 −0
Original line number Diff line number Diff line
@@ -4202,6 +4202,26 @@ static void check_enqueue_throttle(struct cfs_rq *cfs_rq) 
	if (!cfs_bandwidth_used())

		return;



	/* Synchronize hierarchical throttle counter: */

	if (unlikely(!cfs_rq->throttle_uptodate)) {

		struct rq *rq = rq_of(cfs_rq);

		struct cfs_rq *pcfs_rq;

		struct task_group *tg;



		cfs_rq->throttle_uptodate = 1;



		/* Get closest up-to-date node, because leaves go first: */

		for (tg = cfs_rq->tg->parent; tg; tg = tg->parent) {

			pcfs_rq = tg->cfs_rq[cpu_of(rq)];

			if (pcfs_rq->throttle_uptodate)

				break;

		}

		if (tg) {

			cfs_rq->throttle_count = pcfs_rq->throttle_count;

			cfs_rq->throttled_clock_task = rq_clock_task(rq);

		}

	}



	/* an active group must be handled by the update_curr()->put() path */

	if (!cfs_rq->runtime_enabled || cfs_rq->curr)

		return;

kernel/sched/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -437,7 +437,7 @@ struct cfs_rq { 


	u64 throttled_clock, throttled_clock_task;

	u64 throttled_clock_task_time;

	int throttled, throttle_count;

	int throttled, throttle_count, throttle_uptodate;

	struct list_head throttled_list;

#endif /* CONFIG_CFS_BANDWIDTH */

#endif /* CONFIG_FAIR_GROUP_SCHED */