[PATCH 1/8] drm/sched: Add locking to drm_sched_entity_modify_sched

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>

Without the locking amdgpu currently can race between
amdgpu_ctx_set_entity_priority() (via drm_sched_entity_modify_sched()) and
drm_sched_job_arm(), leading to the latter accesing potentially
inconsitent entity->sched_list and entity->num_sched_list pair.

v2:
 * Improve commit message. (Philipp)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
Fixes: b37aced31eb0 ("drm/scheduler: implement a function to modify sched list")
Cc: Christian König <christian.koenig at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Luben Tuikov <ltuikov89 at gmail.com>
Cc: Matthew Brost <matthew.brost at intel.com>
Cc: David Airlie <airlied at gmail.com>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: dri-devel at lists.freedesktop.org
Cc: Philipp Stanner <pstanner at redhat.com>
Cc: <stable at vger.kernel.org> # v5.7+
---
 drivers/gpu/drm/scheduler/sched_entity.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 58c8161289fe..ae8be30472cd 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -133,8 +133,10 @@ void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
 {
 	WARN_ON(!num_sched_list || !sched_list);
 
+	spin_lock(&entity->rq_lock);
 	entity->sched_list = sched_list;
 	entity->num_sched_list = num_sched_list;
+	spin_unlock(&entity->rq_lock);
 }
 EXPORT_SYMBOL(drm_sched_entity_modify_sched);
 
-- 
2.46.0