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

Christian König <christian.koenig@xxxxxxx> · Mon, 20 Jan 2020 11:59:41 +0100

Am 20.01.20 um 11:51 schrieb 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@xxxxxxxxxxxxxx>

Reviewed-by: Christian König <christian.koenig@xxxxxxx>, do you want to 
merge through drm-misc-next or should I push it to amd-staging-drm-next?

Regards,
Christian.

---
  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;
  }

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