The following commit has been merged into the sched/urgent branch of tip:

Commit-ID: 5e2d2cc2588bd3307ce3937acbc2ed03c830a861 Gitweb: https://git.kernel.org/tip/5e2d2cc2588bd3307ce3937acbc2ed03c830a861 Author: Liangyan liangyan.peng@linux.alibaba.com AuthorDate: Mon, 26 Aug 2019 20:16:33 +08:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Tue, 03 Sep 2019 08:55:07 +02:00

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: 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 --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bc9cfea..500f5db 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -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;