[PATCH] drm/etnaviv: Protect the scheduler's pending list with its lock

[Maíra Canal]

Commit 704d3d60fec4 ("drm/etnaviv: don't block scheduler when GPU is still
active") ensured that active jobs are returned to the pending list when
extending the timeout. However, it didn't use the pending list's lock to
manipulate the list, which causes a race condition as the scheduler's
workqueues are running.

Hold the lock while manipulating the scheduler's pending list to prevent
a race.

Cc: stable at vger.kernel.org
Fixes: 704d3d60fec4 ("drm/etnaviv: don't block scheduler when GPU is still active")
Signed-off-by: Maíra Canal <mcanal at igalia.com>
---
Hi,

I'm proposing this workaround patch to address the race-condition caused
by manipulating the pending list without using its lock. Although I
understand this isn't a complete solution (see [1]), it's not reasonable
to backport the new DRM stat series [2] to the stable branches.

Therefore, I believe the best solution is backporting this fix to the
stable branches, which will fix the race and will keep adding the job
back to the pending list (which will avoid most memory leaks).

[1] https://lore.kernel.org/dri-devel/bcc0ed477f8a6f3bb06665b1756bcb98fb7af871.camel@mailbox.org/
[2] https://lore.kernel.org/dri-devel/20250530-sched-skip-reset-v2-0-c40a8d2d8daa@igalia.com/

Best Regards,
- Maíra
---
 drivers/gpu/drm/etnaviv/etnaviv_sched.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_sched.c b/drivers/gpu/drm/etnaviv/etnaviv_sched.c
index 76a3a3e517d8..71e2e6b9d713 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_sched.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_sched.c
@@ -35,6 +35,7 @@ static enum drm_gpu_sched_stat etnaviv_sched_timedout_job(struct drm_sched_job
 							  *sched_job)
 {
 	struct etnaviv_gem_submit *submit = to_etnaviv_submit(sched_job);
+	struct drm_gpu_scheduler *sched = sched_job->sched;
 	struct etnaviv_gpu *gpu = submit->gpu;
 	u32 dma_addr, primid = 0;
 	int change;
@@ -89,7 +90,9 @@ static enum drm_gpu_sched_stat etnaviv_sched_timedout_job(struct drm_sched_job
 	return DRM_GPU_SCHED_STAT_NOMINAL;
 
 out_no_timeout:
-	list_add(&sched_job->list, &sched_job->sched->pending_list);
+	spin_lock(&sched->job_list_lock);
+	list_add(&sched_job->list, &sched->pending_list);
+	spin_unlock(&sched->job_list_lock);
 	return DRM_GPU_SCHED_STAT_NOMINAL;
 }
 
-- 
2.49.0