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Message-ID: <e160d9ec-5ae3-9003-b38c-3027bce736f4@amd.com>
Date: Wed, 25 Sep 2019 20:09:43 +0000
From: "Grodzovsky, Andrey" <Andrey.Grodzovsky@....com>
To: Steven Price <steven.price@....com>,
Daniel Vetter <daniel@...ll.ch>,
David Airlie <airlied@...ux.ie>,
"Koenig, Christian" <Christian.Koenig@....com>
CC: "Deucher, Alexander" <Alexander.Deucher@....com>,
Nayan Deshmukh <nayan26deshmukh@...il.com>,
Sharat Masetty <smasetty@...eaurora.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] drm: Don't free jobs in wait_event_interruptible()
On 9/25/19 12:07 PM, Andrey Grodzovsky wrote:
> On 9/25/19 12:00 PM, Steven Price wrote:
>
>> On 25/09/2019 16:56, Grodzovsky, Andrey wrote:
>>> On 9/25/19 11:14 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. Unfortunately some free callbacks (notably 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@....com>
>>>> ---
>>>> drivers/gpu/drm/scheduler/sched_main.c | 44
>>>> ++++++++++++++------------
>>>> 1 file changed, 24 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c
>>>> b/drivers/gpu/drm/scheduler/sched_main.c
>>>> index 9a0ee74d82dc..0ed4aaa4e6d1 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;
>>>> -
>>>> -
>>>> - while (!list_empty(&sched->ring_mirror_list)) {
>>>> - struct drm_sched_job *job;
>>>> + return NULL;
>>>> - 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);
>>>> + 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 +696,18 @@ 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());
>>>
>>> Can't we just call drm_sched_cleanup_jobs right here, remove all the
>>> conditions in wait_event_interruptible (make it always true) and after
>>> drm_sched_cleanup_jobs is called test for all those conditions and
>>> return to sleep if they evaluate to false ? drm_sched_cleanup_jobs is
>>> called unconditionally inside wait_event_interruptible anyway...
>>> This is
>>> more of a question to Christian.
>> Christian may know better than me, but I think those conditions need to
>> be in wait_event_interruptible() to avoid race conditions. If we simply
>> replace all the conditions with a literal "true" then
>> wait_event_interruptible() will never actually sleep.
>>
>> Steve
>
> Yes you right, it won't work as I missed that condition is evaluated
> as first step in wait_event_interruptible before it sleeps.
>
> Andrey
Another idea - what about still just relocating drm_sched_cleanup_jobs
to after wait_event_interruptible and also call it in drm_sched_fini so
for the case when it will not be called from drm_sched_main due to
conditions not evaluating to true it eventually be called last time
from drm_sched_fini. I mean - the refactor looks ok to me but the code
becomes somewhat confusing this way to grasp.
Andrey
>
>
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