On 26/06/20 13:38, Patrick Bellasi wrote: > On Thu, Jun 25, 2020 at 17:43:52 +0200, Qais Yousef <qais.you...@arm.com> > wrote... >> @@ -994,9 +1013,16 @@ static inline void uclamp_rq_dec_id(struct rq *rq, >> struct task_struct *p, >> lockdep_assert_held(&rq->lock); >> >> bucket = &uc_rq->bucket[uc_se->bucket_id]; >> - SCHED_WARN_ON(!bucket->tasks); >> - if (likely(bucket->tasks)) >> - bucket->tasks--; >> + >> + /* >> + * This could happen if sched_uclamp_used was enabled while the >> + * current task was running, hence we could end up with unbalanced call >> + * to uclamp_rq_dec_id(). >> + */ >> + if (unlikely(!bucket->tasks)) >> + return; >> + >> + bucket->tasks--; >> uc_se->active = false; > > In this chunk you are indeed changing the code. > > Are we sure there are not issues with patterns like: > > enqueue(taskA) > // uclamp gets enabled > enqueue(taskB) > dequeue(taskA) > // bucket->tasks is now 0 > dequeue(taskB) > > TaskB has been enqueued with with uclamp enabled, thus it > has got uc_se->active=True and enforced its clamp value at RQ level. > > But with your change above we don't reset that anymore. >
Harumph indeed... > As per my previous proposal: why not just removing the SCHED_WARN_ON? > That's the only real problem in the code above, since now we are not > more granted to have balanced inc/dec. > The SCHED_WARN_ON is gone, were you thinking of something else?
