[PATCH] drm/panfrost: Handle resetting on timeout better

[Steven Price]

Panfrost uses multiple schedulers (one for each slot, so 2 in reality),
and on a timeout has to stop all the schedulers to safely perform a
reset. However more than one scheduler can trigger a timeout at the same
time. This race condition results in jobs being freed while they are
still in use.

Modify drm_sched_stop() to call cancel_delayed_work_sync() when stopping
a different scheduler to the one belonging to the passed in job.
panfrost_job_timedout() is also modified to only allow one thread at a
time to handle the reset. Any subsequent threads simply return assuming
that the first thread will handle the situation.

Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
 drivers/gpu/drm/panfrost/panfrost_device.h |  2 ++
 drivers/gpu/drm/panfrost/panfrost_job.c    | 11 ++++++++++-
 drivers/gpu/drm/scheduler/sched_main.c     |  5 ++++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
index f503c566e99f..6441c7fba6c4 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.h
+++ b/drivers/gpu/drm/panfrost/panfrost_device.h
@@ -99,6 +99,8 @@ struct panfrost_device {
 		unsigned long cur_volt;
 		struct panfrost_devfreq_slot slot[NUM_JOB_SLOTS];
 	} devfreq;
+
+	bool is_resetting;
 };
 
 struct panfrost_mmu {
diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
index 05c85f45a0de..1b2019e08b43 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -388,13 +388,21 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
 
 	mutex_lock(&pfdev->reset_lock);
 
+	if (pfdev->is_resetting) {
+		mutex_unlock(&pfdev->reset_lock);
+		return;
+	}
+	pfdev->is_resetting = true;
+
+	mutex_unlock(&pfdev->reset_lock);
+
 	for (i = 0; i < NUM_JOB_SLOTS; i++)
 		drm_sched_stop(&pfdev->js->queue[i].sched, sched_job);
 
 	if (sched_job)
 		drm_sched_increase_karma(sched_job);
 
-	/* panfrost_core_dump(pfdev); */
+	mutex_lock(&pfdev->reset_lock);
 
 	panfrost_devfreq_record_transition(pfdev, js);
 	panfrost_device_reset(pfdev);
@@ -406,6 +414,7 @@ static void panfrost_job_timedout(struct drm_sched_job *sched_job)
 	for (i = 0; i < NUM_JOB_SLOTS; i++)
 		drm_sched_start(&pfdev->js->queue[i].sched, true);
 
+	pfdev->is_resetting = false;
 	mutex_unlock(&pfdev->reset_lock);
 }
 
diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 148468447ba9..bc6d1862ec8a 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -415,7 +415,10 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
 	 * this TDR finished and before the newly restarted jobs had a
 	 * chance to complete.
 	 */
-	cancel_delayed_work(&sched->work_tdr);
+	if (bad->sched != sched)
+		cancel_delayed_work_sync(&sched->work_tdr);
+	else
+		cancel_delayed_work(&sched->work_tdr);
 }
 
 EXPORT_SYMBOL(drm_sched_stop);
-- 
2.20.1