On Tue, Aug 20, 2019 at 11:54:20AM +0100, Valentin Schneider wrote: > 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/BANLkTi=NmCxKX6EbDQcJYDJ5kKyG2N1ssw@xxxxxxxxxxxxxx > > Cc: <stable@xxxxxxxxxxxxxxx> > Fixes: ec12cb7f31e2 ("sched: Accumulate per-cfs_rq cpu usage and charge against bandwidth") > Reported-by: Liangyan <liangyan.peng@xxxxxxxxxxxxxxxxx> > Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx> Thanks! > --- > 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 >
