linux-kernel - Re: [PATCH] drm: Don't free jobs in wait_event

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Date:   Thu, 26 Sep 2019 14:58:42 +0000
From:   "Grodzovsky, Andrey" <Andrey.Grodzovsky@....com>
To:     "Koenig, Christian" <Christian.Koenig@....com>,
        Steven Price <steven.price@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        Nayan Deshmukh <nayan26deshmukh@...il.com>,
        Sharat Masetty <smasetty@...eaurora.org>
Subject: Re: [PATCH] drm: Don't free jobs in wait_event_interruptible()


On 9/26/19 3:07 AM, Koenig, Christian wrote:
> Am 25.09.19 um 17:14 schrieb Steven Price:
>> 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);
> This is probably better done after taking the lock, apart from that
> looks good to me.
>
> Christian.


Why is it necessary if insertion and removal from the ring_mirror_list 
are only done from the same scheduler thread ?

Andrey


>
>> -		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());
>> +
>> +		while (cleanup_job) {
>> +			sched->ops->free_job(cleanup_job);
>> +			cleanup_job = drm_sched_get_cleanup_job(sched);
>> +		}
>>    
>>    		if (!entity)
>>    			continue;