[PATCH v2] drm: Don't free jobs in wait_event_interruptible()

From: Steven Price
Date: Thu Sep 26 2019 - 05:56:29 EST


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@xxxxxxx>
---

Changes from v1:
* Move list_first_entry_or_null() within the lock

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());
+
+ while (cleanup_job) {
+ sched->ops->free_job(cleanup_job);
+ cleanup_job = drm_sched_get_cleanup_job(sched);
+ }

if (!entity)
continue;
--
2.20.1