Xunlei Pang <xlp...@linux.alibaba.com> writes:
> Hi Cong,
>
> On 7/28/18 8:24 AM, Cong Wang wrote:
>> Each time we sync cfs_rq->runtime_expires with cfs_b->runtime_expires,
>> we should sync its ->expires_seq too. However it is missing
>> for distribute_cfs_runtime(), especially the slack timer call path.
>
> I don't think it's a problem, as expires_seq will get synced in
> assign_cfs_rq_runtime().
>
> Thanks,
> Xunlei
It does seem unlikely to actually come up since the cfs_rq would have to
not run until the period was expired-locally-but-not-globally, but
there's no reason to not fix it.
>
>>
>> Fixes: 512ac999d275 ("sched/fair: Fix bandwidth timer clock drift condition")
>> Cc: Xunlei Pang <xlp...@linux.alibaba.com>
>> Cc: Ben Segall <bseg...@google.com>
>> Cc: Linus Torvalds <torva...@linux-foundation.org>
>> Cc: Peter Zijlstra <pet...@infradead.org>
>> Cc: Thomas Gleixner <t...@linutronix.de>
>> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
>> ---
>> kernel/sched/fair.c | 12 ++++++++----
>> 1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 2f0a0be4d344..910c50db3d74 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -4857,7 +4857,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
>> }
>>
>> static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
>> - u64 remaining, u64 expires)
>> + u64 remaining, u64 expires, int expires_seq)
>> {
>> struct cfs_rq *cfs_rq;
>> u64 runtime;
>> @@ -4880,6 +4880,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth
>> *cfs_b,
>>
>> cfs_rq->runtime_remaining += runtime;
>> cfs_rq->runtime_expires = expires;
>> + cfs_rq->expires_seq = expires_seq;
>>
>> /* we check whether we're throttled above */
>> if (cfs_rq->runtime_remaining > 0)
>> @@ -4905,7 +4906,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth
>> *cfs_b,
>> static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int
>> overrun)
>> {
>> u64 runtime, runtime_expires;
>> - int throttled;
>> + int throttled, expires_seq;
>>
>> /* no need to continue the timer with no bandwidth constraint */
>> if (cfs_b->quota == RUNTIME_INF)
>> @@ -4933,6 +4934,7 @@ static int do_sched_cfs_period_timer(struct
>> cfs_bandwidth *cfs_b, int overrun)
>> cfs_b->nr_throttled += overrun;
>>
>> runtime_expires = cfs_b->runtime_expires;
>> + expires_seq = cfs_b->expires_seq;
>>
>> /*
>> * This check is repeated as we are holding onto the new bandwidth while
>> @@ -4946,7 +4948,7 @@ static int do_sched_cfs_period_timer(struct
>> cfs_bandwidth *cfs_b, int overrun)
>> raw_spin_unlock(&cfs_b->lock);
>> /* we can't nest cfs_b->lock while distributing bandwidth */
>> runtime = distribute_cfs_runtime(cfs_b, runtime,
>> - runtime_expires);
>> + runtime_expires, expires_seq);
>> raw_spin_lock(&cfs_b->lock);
>>
>> throttled = !list_empty(&cfs_b->throttled_cfs_rq);
>> @@ -5055,6 +5057,7 @@ static __always_inline void
>> return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
>> static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
>> {
>> u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
>> + int expires_seq;
>> u64 expires;
>>
>> /* confirm we're still not at a refresh boundary */
>> @@ -5068,12 +5071,13 @@ static void do_sched_cfs_slack_timer(struct
>> cfs_bandwidth *cfs_b)
>> runtime = cfs_b->runtime;
>>
>> expires = cfs_b->runtime_expires;
>> + expires_seq = cfs_b->expires_seq;
>> raw_spin_unlock(&cfs_b->lock);
>>
>> if (!runtime)
>> return;
>>
>> - runtime = distribute_cfs_runtime(cfs_b, runtime, expires);
>> + runtime = distribute_cfs_runtime(cfs_b, runtime, expires, expires_seq);
>>
>> raw_spin_lock(&cfs_b->lock);
>> if (expires == cfs_b->runtime_expires)
>>
