Re: [PATCH 2/2] drm/sched: document the RCU dependency

[Philipp Stanner <phasta@mailbox.org>]

On Mon, 2026-09-14 at 20:27 +0200, Christian König wrote:
> Tvrkos patches added RCU protection to the returned strings from

*Tvrtko ;)

Anyways, which patches? Better add a commit ID?

> get_timeline_name()/get_driver_name() callbacks of the dma_fence
> backends.
> 
> This fixed use after free problems for a couple of drivers, but we never
> documented the consequences for the drm_sched_fence.
> 
> Add a few words on the function documentation to note that we need an
> RCU grace period between signaling the last scheduler fence and

s/scheduler fence/hardware-fence

:D

> scheduler teardown.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>

with the above:

Acked-by: Philipp Stanner <phasta@kernel.org>

> ---
>  drivers/gpu/drm/scheduler/sched_main.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 6cb6f95464938..f73c5141b4e5c 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -1203,6 +1203,11 @@ static void drm_sched_cancel_remaining_jobs(struct drm_gpu_scheduler *sched)
>   * is implemented, all jobs will be canceled through it and afterwards cleaned
>   * up through &struct drm_sched_backend_ops.free_job. If cancel_job is not
>   * implemented, memory could leak.
> + *
> + * The user must wait one RCU grace period between signaling the last hardware-
> + * fence and calling this function because the timeline name returned by
> + * scheduler fences must stay valid until all readers have exited their RCU read
> + * side critical section.
>   */
>  void drm_sched_fini(struct drm_gpu_scheduler *sched)
>  {