blocking ops in drm_sched_cleanup_jobs()

[Steven Price]

On 24/09/2019 10:55, Koenig, Christian wrote:
> Sorry for the delayed response, have been busy on other stuff last week.
> 
> Am 17.09.19 um 14:46 schrieb Steven Price:
>> On 17/09/2019 09:42, Koenig, Christian wrote:
>>> Hi Steven,
>>>
>>> thought about that issue a bit more and I think I came up with a 
>>> solution.
>>>
>>> What you could do is to split up drm_sched_cleanup_jobs() into two
>>> functions.
>>>
>>> One that checks if jobs to be cleaned up are present and one which does
>>> the actual cleanup.
>>>
>>> This way we could call drm_sched_cleanup_jobs() outside of the
>>> wait_event_interruptible().
>>
>> Yes that seems like a good solution - there doesn't seem to be a good 
>> reason why the actual job cleanup needs to be done within the 
>> wait_event_interruptible() condition. I did briefly attempt that 
>> before, but I couldn't work out exactly what the condition is which 
>> should cause the wake (my initial attempt caused continuous wake-ups).
> 
> Basically you need something like the following:
> 
> 1. Test is timeout worker is running:
> 
> if (sched->timeout != MAX_SCHEDULE_TIMEOUT &&
>      !cancel_delayed_work(&sched->work_tdr))
>          return false;
> 
> 2. Test if there is any job ready to be cleaned up.
> 
> job = list_first_entry_or_null(&sched->ring_mirror_list, struct 
> drm_sched_job, node);
> if (!job || !dma_fence_is_signaled(&job->s_fence->finished))
>      return false;
> 
> That should basically do it.

Thanks for the pointers. I wasn't sure if the "queue timeout for next
job" part was necessary or not if step 2 above returns false.

I've been testing the following patch which simply pulls the
sched->ops->free_job() out of the wait_event_interruptible().

I'll try with just the tests you've described.

----8<-----
>From 873c1816394beee72904e64aa2ee0f169e768d76 Mon Sep 17 00:00:00 2001
From: Steven Price <steven.price at arm.com>
Date: Mon, 23 Sep 2019 11:08:50 +0100
Subject: [PATCH] drm: Don't free jobs in wait_event_interruptible()

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 at arm.com>
---
 drivers/gpu/drm/scheduler/sched_main.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 9a0ee74d82dc..bf9b4931ddfd 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -622,20 +622,21 @@ 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)
 {
 	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)) {
@@ -651,7 +652,7 @@ static void drm_sched_cleanup_jobs(struct drm_gpu_scheduler *sched)
 		list_del_init(&job->node);
 		spin_unlock_irqrestore(&sched->job_list_lock, flags);
 
-		sched->ops->free_job(job);
+		return job;
 	}
 
 	/* queue timeout for next job */
@@ -659,6 +660,7 @@ static void drm_sched_cleanup_jobs(struct drm_gpu_scheduler *sched)
 	drm_sched_start_timeout(sched);
 	spin_unlock_irqrestore(&sched->job_list_lock, flags);
 
+	return NULL;
 }
 
 /**
@@ -698,12 +700,18 @@ 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;
-- 
2.20.1