Commit 5e2d2cc2 authored Aug 26, 2019 by Liangyan Committed by Ingo Molnar Sep 03, 2019

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



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: Liangyan <liangyan.peng@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Ben 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: Ingo Molnar <mingo@kernel.org>

parent 089cf7f6

kernel/sched/fair.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -4470,6 +4470,8 @@ 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
		@@ -4673,6 +4675,9 @@ 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;

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