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

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Date:   Thu, 26 Sep 2019 10:47:13 +0100
From:   Steven Price <steven.price@....com>
To:     "Koenig, Christian" <Christian.Koenig@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>
Cc:     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>,
        Nayan Deshmukh <nayan26deshmukh@...il.com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>
Subject: Re: [PATCH] drm: Don't free jobs in wait_event_interruptible()

On 26/09/2019 08:07, 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.

It wasn't previously protected by the lock - but I don't see any harm so
I'll post a v2.

Steve