On Tue, 13 Jun 2023 11:28:45 +0200
Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> wrote:
> drm_sched_entity_kill_jobs_cb() logic is omitting the last fence popped
> from the dependency array that was waited upon before
> drm_sched_entity_kill() was called (drm_sched_entity::dependency field),
> so we're basically waiting for all dependencies except one.
>
> In theory, this wait shouldn't be needed because resources should have
> their users registered to the dma_resv object, thus guaranteeing that
> future jobs wanting to access these resources wait on all the previous
> users (depending on the access type, of course). But we want to keep
> these explicit waits in the kill entity path just in case.
>
> Let's make sure we keep all dependencies in the array in
> drm_sched_job_dependency(), so we can iterate over the array and wait
> in drm_sched_entity_kill_jobs_cb().
>
> We also make sure we wait on drm_sched_fence::finished if we were asked
> to wait on drm_sched_fence::scheduled, but the intent was probably to
> delegate the wait to the GPU, but we want resources to be completely
> idle when killing jobs.
>
> v3:
> - Always wait for drm_sched_fence::finished fences in
> drm_sched_entity_kill_jobs_cb() when we see a sched_fence
>
> v2:
> - Don't evict deps in drm_sched_job_dependency()
>
> Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> Suggested-by: "Christian König" <christian.koenig@xxxxxxx>
> Cc: Frank Binns <frank.binns@xxxxxxxxxx>
> Cc: Sarah Walker <sarah.walker@xxxxxxxxxx>
> Cc: Donald Robson <donald.robson@xxxxxxxxxx>
> Cc: Luben Tuikov <luben.tuikov@xxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> Cc: "Christian König" <christian.koenig@xxxxxxx>
> ---
> drivers/gpu/drm/scheduler/sched_entity.c | 28 ++++++++++++++++++++----
> 1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index 68e807ae136a..bc1bc3d47f7f 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -176,13 +176,24 @@ static void drm_sched_entity_kill_jobs_cb(struct dma_fence *f,
> {
> struct drm_sched_job *job = container_of(cb, struct drm_sched_job,
> finish_cb);
> + unsigned long index;
> int r;
>
> dma_fence_put(f);
>
> /* Wait for all dependencies to avoid data corruptions */
> - while (!xa_empty(&job->dependencies)) {
> - f = xa_erase(&job->dependencies, job->last_dependency++);
> + xa_for_each(&job->dependencies, index, f) {
> + struct drm_sched_fence *s_fence = to_drm_sched_fence(f);
> +
> + /* Make sure we wait for the finished fence here, so we can
> + * guarantee that any job we depend on that is still accessing
> + * resources is done before we signal this job finished fence
> + * and unblock further accesses on those resources.
> + */
> + if (s_fence && f == &s_fence->scheduled)
> + f = &s_fence->finished;
Oops. There's a use-after-free+leak bug here: when switching from
scheduled to finished fence, we need to grab a ref on the finished
fence and release the one we had on the scheduled fence.
Sending a v4 to fix that.
> +
> + xa_erase(&job->dependencies, index);
> r = dma_fence_add_callback(f, &job->finish_cb,
> drm_sched_entity_kill_jobs_cb);
> if (!r)
> @@ -415,8 +426,17 @@ static struct dma_fence *
> drm_sched_job_dependency(struct drm_sched_job *job,
> struct drm_sched_entity *entity)
> {
> - if (!xa_empty(&job->dependencies))
> - return xa_erase(&job->dependencies, job->last_dependency++);
> + struct dma_fence *f;
> +
> + /* We keep the fence around, so we can iterate over all dependencies
> + * in drm_sched_entity_kill_jobs_cb() to ensure all deps are signaled
> + * before killing the job.
> + */
> + f = xa_load(&job->dependencies, job->last_dependency);
> + if (f) {
> + job->last_dependency++;
> + return dma_fence_get(f);
> + }
>
> if (job->sched->ops->prepare_job)
> return job->sched->ops->prepare_job(job, entity);
