[PATCH] drm/scheduler: fix inconsistent locking of job_list_lock

[Lucas Stach]

1db8c142b6c5 (drm/scheduler: Add drm_sched_suspend/resume_timeout()) made
the job_list_lock IRQ safe in as the suspend/resume calls were expected to
be called from IRQ context. This usage never materialized in upstream.
Instead amdgpu started locking the job_list_lock in an IRQ unsafe way in
amdgpu_ib_preempt_mark_partial_job() and amdgpu_ib_preempt_job_recovery(),
which leads to potential deadlock if one would actually start to call the
drm_sched_suspend/resume_timeout functions from IRQ context.

As no current user needs the locking to be IRQ safe, the local IRQ
disable/enable is pure overhead. Fix the inconsistent locking by changing
all uses of job_list_lock to use the IRQ unsafe locking primitives.

Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
---
 drivers/gpu/drm/scheduler/sched_main.c | 38 ++++++++++----------------
 1 file changed, 15 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 3c57e84222ca..d1b24444dd99 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -220,8 +220,7 @@ EXPORT_SYMBOL(drm_sched_fault);
  *
  * Suspend the delayed work timeout for the scheduler. This is done by
  * modifying the delayed work timeout to an arbitrary large value,
- * MAX_SCHEDULE_TIMEOUT in this case. Note that this function can be
- * called from an IRQ context.
+ * MAX_SCHEDULE_TIMEOUT in this case.
  *
  * Returns the timeout remaining
  *
@@ -250,43 +249,39 @@ EXPORT_SYMBOL(drm_sched_suspend_timeout);
  * @sched: scheduler instance for which to resume the timeout
  * @remaining: remaining timeout
  *
- * Resume the delayed work timeout for the scheduler. Note that
- * this function can be called from an IRQ context.
+ * Resume the delayed work timeout for the scheduler.
  */
 void drm_sched_resume_timeout(struct drm_gpu_scheduler *sched,
 		unsigned long remaining)
 {
-	unsigned long flags;
-
-	spin_lock_irqsave(&sched->job_list_lock, flags);
+	spin_lock(&sched->job_list_lock);
 
 	if (list_empty(&sched->ring_mirror_list))
 		cancel_delayed_work(&sched->work_tdr);
 	else
 		mod_delayed_work(system_wq, &sched->work_tdr, remaining);
 
-	spin_unlock_irqrestore(&sched->job_list_lock, flags);
+	spin_unlock(&sched->job_list_lock);
 }
 EXPORT_SYMBOL(drm_sched_resume_timeout);
 
 static void drm_sched_job_begin(struct drm_sched_job *s_job)
 {
 	struct drm_gpu_scheduler *sched = s_job->sched;
-	unsigned long flags;
 
-	spin_lock_irqsave(&sched->job_list_lock, flags);
+	spin_lock(&sched->job_list_lock);
 	list_add_tail(&s_job->node, &sched->ring_mirror_list);
 	drm_sched_start_timeout(sched);
-	spin_unlock_irqrestore(&sched->job_list_lock, flags);
+	spin_unlock(&sched->job_list_lock);
 }
 
 static void drm_sched_job_timedout(struct work_struct *work)
 {
 	struct drm_gpu_scheduler *sched;
 	struct drm_sched_job *job;
-	unsigned long flags;
 
 	sched = container_of(work, struct drm_gpu_scheduler, work_tdr.work);
+
 	job = list_first_entry_or_null(&sched->ring_mirror_list,
 				       struct drm_sched_job, node);
 
@@ -303,9 +298,9 @@ static void drm_sched_job_timedout(struct work_struct *work)
 		}
 	}
 
-	spin_lock_irqsave(&sched->job_list_lock, flags);
+	spin_lock(&sched->job_list_lock);
 	drm_sched_start_timeout(sched);
-	spin_unlock_irqrestore(&sched->job_list_lock, flags);
+	spin_unlock(&sched->job_list_lock);
 }
 
  /**
@@ -368,7 +363,6 @@ EXPORT_SYMBOL(drm_sched_increase_karma);
 void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
 {
 	struct drm_sched_job *s_job, *tmp;
-	unsigned long flags;
 
 	kthread_park(sched->thread);
 
@@ -388,9 +382,9 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
 			 * remove job from ring_mirror_list.
 			 * Locking here is for concurrent resume timeout
 			 */
-			spin_lock_irqsave(&sched->job_list_lock, flags);
+			spin_lock(&sched->job_list_lock);
 			list_del_init(&s_job->node);
-			spin_unlock_irqrestore(&sched->job_list_lock, flags);
+			spin_unlock(&sched->job_list_lock);
 
 			/*
 			 * Wait for job's HW fence callback to finish using s_job
@@ -433,7 +427,6 @@ EXPORT_SYMBOL(drm_sched_stop);
 void drm_sched_start(struct drm_gpu_scheduler *sched, bool full_recovery)
 {
 	struct drm_sched_job *s_job, *tmp;
-	unsigned long flags;
 	int r;
 
 	/*
@@ -462,9 +455,9 @@ void drm_sched_start(struct drm_gpu_scheduler *sched, bool full_recovery)
 	}
 
 	if (full_recovery) {
-		spin_lock_irqsave(&sched->job_list_lock, flags);
+		spin_lock(&sched->job_list_lock);
 		drm_sched_start_timeout(sched);
-		spin_unlock_irqrestore(&sched->job_list_lock, flags);
+		spin_unlock(&sched->job_list_lock);
 	}
 
 	kthread_unpark(sched->thread);
@@ -648,7 +641,6 @@ static struct drm_sched_job *
 drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
 {
 	struct drm_sched_job *job;
-	unsigned long flags;
 
 	/*
 	 * Don't destroy jobs while the timeout worker is running  OR thread
@@ -659,7 +651,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
 	    __kthread_should_park(sched->thread))
 		return NULL;
 
-	spin_lock_irqsave(&sched->job_list_lock, flags);
+	spin_lock(&sched->job_list_lock);
 
 	job = list_first_entry_or_null(&sched->ring_mirror_list,
 				       struct drm_sched_job, node);
@@ -673,7 +665,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
 		drm_sched_start_timeout(sched);
 	}
 
-	spin_unlock_irqrestore(&sched->job_list_lock, flags);
+	spin_unlock(&sched->job_list_lock);
 
 	return job;
 }
-- 
2.20.1