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.
This will cause other cfs_rq 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; }.
This cast will cause that runtime will be a large number and
cfs_b->runtime will be subtracted to be zero at last.
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 to avoid the above incorrect type cast. Signed-off-by: Liangyan <[email protected]> Reviewed-by: Ben Segall <[email protected]> Reviewed-by: Valentin Schneider <[email protected]> --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bc9cfeaac8bd..ac3ae694d850 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 */ + WARN_ON(cfs_rq->runtime_remaining > 0); + runtime = -cfs_rq->runtime_remaining + 1; if (runtime > remaining) runtime = remaining; -- 2.14.4.44.g2045bb6
