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SubjectRe: [PATCH v4] drm: Don't free jobs in wait_event_interruptible()
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On 9/26/19 11:23 AM, Steven Price wrote:
> On 26/09/2019 16:14, Grodzovsky, Andrey wrote:
>> On 9/26/19 10:16 AM, Steven Price wrote:
>>> drm_sched_cleanup_jobs() attempts to free finished jobs, however because
>>> it is called as the condition of wait_event_interruptible() it must not
>>> sleep. Unfortuantly some free callbacks (notibly for Panfrost) do sleep.
>>>
>>> Instead let's rename drm_sched_cleanup_jobs() to
>>> drm_sched_get_cleanup_job() and simply return a job for processing if
>>> there is one. The caller can then call the free_job() callback outside
>>> the wait_event_interruptible() where sleeping is possible before
>>> re-checking and returning to sleep if necessary.
>>>
>>> Signed-off-by: Steven Price <steven.price@arm.com>
>>> ---
>>> Changes from v3:
>>> * drm_sched_main() re-arms the timeout for the next job after calling
>>> free_job()
>>>
>>> drivers/gpu/drm/scheduler/sched_main.c | 45 +++++++++++++++-----------
>>> 1 file changed, 26 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>>> index 9a0ee74d82dc..148468447ba9 100644
>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>> @@ -622,43 +622,41 @@ static void drm_sched_process_job(struct dma_fence *f, struct dma_fence_cb *cb)
>>> }
>>>
>>> /**
>>> - * drm_sched_cleanup_jobs - destroy finished jobs
>>> + * drm_sched_get_cleanup_job - fetch the next finished job to be destroyed
>>> *
>>> * @sched: scheduler instance
>>> *
>>> - * Remove all finished jobs from the mirror list and destroy them.
>>> + * Returns the next finished job from the mirror list (if there is one)
>>> + * ready for it to be destroyed.
>>> */
>>> -static void drm_sched_cleanup_jobs(struct drm_gpu_scheduler *sched)
>>> +static struct drm_sched_job *
>>> +drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
>>> {
>>> + struct drm_sched_job *job = NULL;
>>> unsigned long flags;
>>>
>>> /* Don't destroy jobs while the timeout worker is running */
>>> if (sched->timeout != MAX_SCHEDULE_TIMEOUT &&
>>> !cancel_delayed_work(&sched->work_tdr))
>>> - return;
>>> -
>>> + return NULL;
>>>
>>> - while (!list_empty(&sched->ring_mirror_list)) {
>>> - struct drm_sched_job *job;
>>> + spin_lock_irqsave(&sched->job_list_lock, flags);
>>>
>>> - job = list_first_entry(&sched->ring_mirror_list,
>>> + job = list_first_entry_or_null(&sched->ring_mirror_list,
>>> struct drm_sched_job, node);
>>> - if (!dma_fence_is_signaled(&job->s_fence->finished))
>>> - break;
>>>
>>> - spin_lock_irqsave(&sched->job_list_lock, flags);
>>> + if (job && dma_fence_is_signaled(&job->s_fence->finished)) {
>>> /* remove job from ring_mirror_list */
>>> list_del_init(&job->node);
>>> - spin_unlock_irqrestore(&sched->job_list_lock, flags);
>>> -
>>> - sched->ops->free_job(job);
>>> + } else {
>>> + job = NULL;
>>> + /* queue timeout for next job */
>>> + drm_sched_start_timeout(sched);
>>> }
>>>
>>> - /* queue timeout for next job */
>>> - spin_lock_irqsave(&sched->job_list_lock, flags);
>>> - drm_sched_start_timeout(sched);
>>> spin_unlock_irqrestore(&sched->job_list_lock, flags);
>>>
>>> + return job;
>>> }
>>>
>>> /**
>>> @@ -698,12 +696,21 @@ static int drm_sched_main(void *param)
>>> struct drm_sched_fence *s_fence;
>>> struct drm_sched_job *sched_job;
>>> struct dma_fence *fence;
>>> + struct drm_sched_job *cleanup_job = NULL;
>>>
>>> wait_event_interruptible(sched->wake_up_worker,
>>> - (drm_sched_cleanup_jobs(sched),
>>> + (cleanup_job = drm_sched_get_cleanup_job(sched)) ||
>>> (!drm_sched_blocked(sched) &&
>>> (entity = drm_sched_select_entity(sched))) ||
>>> - kthread_should_stop()));
>>> + kthread_should_stop());
>>> +
>>> + while (cleanup_job) {
>>> + sched->ops->free_job(cleanup_job);
>>> + /* queue timeout for next job */
>>> + drm_sched_start_timeout(sched);
>>> +
>>> + cleanup_job = drm_sched_get_cleanup_job(sched);
>>> + }
>>
>> Why drm_sched_start_timeout is called both here and inside
>> drm_sched_get_cleanup_job ? And also why call it multiple times in the
>> loop instead of only once after the loop is done  ?
> Christian pointed out to be that the first thing
> drm_sched_get_cleanup_job does is call cancel_delayed_work(), and if
> that returns false then it bails out with a NULL return. So to actually
> get another job (if one exists) the timeout has to be restarted.


For this case where timeout work already in progress note that
drm_sched_job_timedout restarts the timeout in it's end so it should be
ok to restart the timeout unconditionally inside
drm_sched_get_cleanup_job as it was done before.


>
> It's also necessary to restart the timeout in the case where the return
> is NULL which is handled in the function itself.
>
> TBH I'm not sure whether this while loop is worth it - it may be better
> to replace it with simply:
>
> if (cleanup_job) {
> sched->ops->free_job(cleanup_job);
> /* queue timeout for next job */
> drm_sched_start_timeout(sched);
> }
>
> The outer loop would then handle the next call to
> drm_sched_get_cleanup_job() as necessary.


What outer loop ?

Andrey

>
> Steve
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