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drm/sched: Fix racy access to drm_sched_entity.dependency

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The drm_sched_job_unschedulable trace point can access
entity->dependency after it was cleared by the callback
installed in drm_sched_entity_add_dependency_cb, causing:

BUG: kernel NULL pointer dereference, address: 0000000000000020
[...]
Workqueue: comp_1.1.0 drm_sched_run_job_work [gpu_sched]
RIP: 0010:trace_event_raw_event_drm_sched_job_unschedulable+0x70/0xd0 [gpu_sched]

To fix this we either need to keep a reference to the fence before
setting up the callbacks, or move the trace_drm_sched_job_unschedulable
calls into drm_sched_entity_add_dependency_cb where they can be
done earlier.

Fixes: 76d97c870f ("drm/sched: Trace dependencies for GPU jobs")

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://lore.kernel.org/r/20250901124032.1955-1-pierre-eric.pelloux-prayer@amd.com
This commit is contained in:
Pierre-Eric Pelloux-Prayer 2025-09-01 14:40:32 +02:00 committed by Philipp Stanner
parent a69997be44
commit b2b8af21fe
1 changed files with 7 additions and 4 deletions
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11
drivers/gpu/drm/scheduler/sched_entity.c
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@ -391,7 +391,8 @@ EXPORT_SYMBOL(drm_sched_entity_set_priority);
* Add a callback to the current dependency of the entity to wake up the
* scheduler when the entity becomes available.
*/
static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity)
static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity,
struct drm_sched_job *sched_job)
{
struct drm_gpu_scheduler *sched = entity->rq->sched;
struct dma_fence *fence = entity->dependency;
@ -421,6 +422,10 @@ static bool drm_sched_entity_add_dependency_cb(struct drm_sched_entity *entity)
entity->dependency = fence;
}
if (trace_drm_sched_job_unschedulable_enabled() &&
!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &entity->dependency->flags))
trace_drm_sched_job_unschedulable(sched_job, entity->dependency);
if (!dma_fence_add_callback(entity->dependency, &entity->cb,
drm_sched_entity_wakeup))
return true;
@ -461,10 +466,8 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity)
while ((entity->dependency =
drm_sched_job_dependency(sched_job, entity))) {
if (drm_sched_entity_add_dependency_cb(entity)) {
trace_drm_sched_job_unschedulable(sched_job, entity->dependency);
if (drm_sched_entity_add_dependency_cb(entity, sched_job))
return NULL;
}
}
/* skip jobs from entity that marked guilty */