[PATCH 0/2] drm/sched: Add bloody spinlocks

[PATCH 0/2] drm/sched: Add bloody spinlocks

[Philipp Stanner]

The scheduler wouldn't be the scheduler if there weren't functions like
drm_sched_job_arm() being called probably a few thousand times per
second without taking proper locks, just racing wildly.

This series adds the proper locks to drm_sched_job_init() and
drm_sched_job_arm().

Philipp Stanner (2):
  drm/sched: Use proper locks in drm_sched_job_arm()
  drm/sched: Use proper locks for drm_sched_job_init()

 drivers/gpu/drm/scheduler/sched_main.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

-- 
2.49.0

[PATCH 1/2] drm/sched: Use proper locks in drm_sched_job_arm()

[Philipp Stanner]

drm_sched_job_arm() is just racing when dereferencing entity and
runqueue.

Add the proper spinlocks.

Cc: stable@vger.kernel.org # v5.16+
Fixes: dbe48d030b28 ("drm/sched: Split drm_sched_job_init")
Signed-off-by: Philipp Stanner <phasta@kernel.org>
---
 drivers/gpu/drm/scheduler/sched_main.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index c39f0245e3a9..7f938f491b6f 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -859,10 +859,16 @@ void drm_sched_job_arm(struct drm_sched_job *job)
 
 	BUG_ON(!entity);
 	drm_sched_entity_select_rq(entity);
+
+	spin_lock(&entity->lock);
+	spin_lock(&entity->rq->lock);
 	sched = entity->rq->sched;
+	spin_unlock(&entity->rq->lock);
+
+	job->s_priority = entity->priority;
+	spin_unlock(&entity->lock);
 
 	job->sched = sched;
-	job->s_priority = entity->priority;
 
 	drm_sched_fence_init(job->s_fence, job->entity);
 }
-- 
2.49.0

[PATCH 2/2] drm/sched: Use proper locks for drm_sched_job_init()

[Philipp Stanner]

drm_sched_job_init() is just racing when checking an entity's runqueue, without
taking the proper spinlock.

Add the lock.

Cc: stable@vger.kernel.org # 6.7+
Fixes: 56e449603f0a ("drm/sched: Convert the GPU scheduler to variable number of run-queues")
Signed-off-by: Philipp Stanner <phasta@kernel.org>
---
 drivers/gpu/drm/scheduler/sched_main.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 7f938f491b6f..30028054385f 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -799,7 +799,12 @@ int drm_sched_job_init(struct drm_sched_job *job,
 		       u32 credits, void *owner,
 		       uint64_t drm_client_id)
 {
-	if (!entity->rq) {
+	struct drm_sched_rq *rq;
+
+	spin_lock(&entity->lock);
+	rq = entity->rq;
+	spin_unlock(&entity->lock);
+	if (!rq) {
 		/* This will most likely be followed by missing frames
 		 * or worse--a blank screen--leave a trail in the
 		 * logs, so this can be debugged easier.
-- 
2.49.0