Turns out a cfs_rq->runtime_remaining can become positive in assign_cfs_rq_runtime(), but this codepath has no call to unthrottle_cfs_rq().
This can leave us in a situation where we have a throttled cfs_rq with positive ->runtime_remaining, which breaks the math in distribute_cfs_runtime(): this function expects a negative value so that it may safely negate it into a positive value. Add the missing unthrottle_cfs_rq(). While at it, add a WARN_ON where we expect negative values, and pull in a comment from the mailing list that didn't make it in [1]. [1]: https://lkml.kernel.org/r/[email protected] Cc: <[email protected]> Fixes: ec12cb7f31e2 ("sched: Accumulate per-cfs_rq cpu usage and charge against bandwidth") Reported-by: Liangyan <[email protected]> Signed-off-by: Valentin Schneider <[email protected]> --- kernel/sched/fair.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1054d2cf6aaa..219ff3f328e5 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4385,6 +4385,11 @@ static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq) return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time; } +static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq) +{ + return cfs_bandwidth_used() && cfs_rq->throttled; +} + /* returns 0 on failure to allocate runtime */ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq) { @@ -4411,6 +4416,9 @@ static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq) cfs_rq->runtime_remaining += amount; + if (cfs_rq->runtime_remaining > 0 && cfs_rq_throttled(cfs_rq)) + unthrottle_cfs_rq(cfs_rq); + return cfs_rq->runtime_remaining > 0; } @@ -4439,11 +4447,6 @@ void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec) __account_cfs_rq_runtime(cfs_rq, delta_exec); } -static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq) -{ - return cfs_bandwidth_used() && cfs_rq->throttled; -} - /* check whether cfs_rq, or any parent, is throttled */ static inline int throttled_hierarchy(struct cfs_rq *cfs_rq) { @@ -4628,6 +4631,10 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b, u64 remaining) if (!cfs_rq_throttled(cfs_rq)) goto next; + /* By the above check, this should never be true */ + WARN_ON(cfs_rq->runtime_remaining > 0); + + /* Pick the minimum amount to return to a positive quota state */ runtime = -cfs_rq->runtime_remaining + 1; if (runtime > remaining) runtime = remaining; -- 2.22.0
