3.16.78-rc1 review patch. If anyone has any objections, please let me know.
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From: Liangyan liangyan.peng@linux.alibaba.com
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: 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: xlpang@linux.alibaba.com Fixes: d3d9dc330236 ("sched: Throttle entities exceeding their allowed bandwidth") Link: https://lkml.kernel.org/r/20190826121633.6538-1-liangyan.peng@linux.alibaba.... Signed-off-by: Ingo Molnar mingo@kernel.org [bwh: Backported to 3.16: Open-code SCHED_WARN_ON().] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3271,6 +3271,8 @@ static void __account_cfs_rq_runtime(str 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 @@ -3450,6 +3452,11 @@ static u64 distribute_cfs_runtime(struct if (!cfs_rq_throttled(cfs_rq)) goto next;
+ /* By the above check, this should never be true */ +#ifdef CONFIG_SCHED_DEBUG + WARN_ON_ONCE(cfs_rq->runtime_remaining > 0); +#endif + runtime = -cfs_rq->runtime_remaining + 1; if (runtime > remaining) runtime = remaining;