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Commit 0a3989a5 authored by Liangyan's avatar Liangyan Committed by Greg Kroah-Hartman
Browse files

sched/fair: Don't assign runtime for throttled cfs_rq 



commit 5e2d2cc2588bd3307ce3937acbc2ed03c830a861 upstream.

do_sched_cfs_period_timer() will refill cfs_b runtime and call
distribute_cfs_runtime to unthrottle cfs_rq, sometimes cfs_b->runtime
will allocate all quota to one cfs_rq incorrectly, then other cfs_rqs
attached to this cfs_b can't get runtime and will be throttled.

We find that one throttled cfs_rq has non-negative
cfs_rq->runtime_remaining and cause an unexpetced cast from s64 to u64
in snippet:

  distribute_cfs_runtime() {
    runtime = -cfs_rq->runtime_remaining + 1;
  }

The runtime here will change to a large number and consume all
cfs_b->runtime in this cfs_b period.

According to Ben Segall, the throttled cfs_rq can have
account_cfs_rq_runtime called on it because it is throttled before
idle_balance, and the idle_balance calls update_rq_clock to add time
that is accounted to the task.

This commit prevents cfs_rq to be assgined new runtime if it has been
throttled until that distribute_cfs_runtime is called.

Signed-off-by: default avatarLiangyan <liangyan.peng@linux.alibaba.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Reviewed-by: default avatarBen Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: shanpeic@linux.alibaba.com
Cc: stable@vger.kernel.org
Cc: xlpang@linux.alibaba.com
Fixes: d3d9dc33 ("sched: Throttle entities exceeding their allowed bandwidth")
Link: https://lkml.kernel.org/r/20190826121633.6538-1-liangyan.peng@linux.alibaba.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a2663aaa

kernel/sched/fair.c

+5 −0
Original line number Diff line number Diff line
@@ -3882,6 +3882,8 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) 
	if (likely(cfs_rq->runtime_remaining > 0))

		return;



	if (cfs_rq->throttled)

		return;

	/*

	 * if we're unable to extend our runtime we resched so that the active

	 * hierarchy can be throttled
@@ -4077,6 +4079,9 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b, 
		if (!cfs_rq_throttled(cfs_rq))

			goto next;



		/* By the above check, this should never be true */

		SCHED_WARN_ON(cfs_rq->runtime_remaining > 0);



		runtime = -cfs_rq->runtime_remaining + 1;

		if (runtime > remaining)

			runtime = remaining;