[PATCH v2] Revert "drm/scheduler: Avoid accessing freed bad job."

[Alex Deucher]

+ dri-devel

Since scheduler is a shared component, please add dri-devel on all
scheduler patches.

On Wed, Aug 18, 2021 at 7:21 AM Jingwen Chen <Jingwen.Chen2 at amd.com> wrote:
>
> [Why]
> for bailing job, this commit will delete it from pending list thus the
> bailing job will never have a chance to be resubmitted even in advance
> tdr mode.
>
> [How]
> after embeded hw_fence into amdgpu_job is done, the race condition that
> this commit tries to work around is completely solved.So revert this
> commit.
> This reverts commit 135517d3565b48f4def3b1b82008bc17eb5d1c90.
> v2:
> add dma_fence_get/put() around timedout_job to avoid concurrent delete
> during processing timedout_job
>
> Signed-off-by: Jingwen Chen <Jingwen.Chen2 at amd.com>
> ---
>  drivers/gpu/drm/scheduler/sched_main.c | 23 +++++------------------
>  1 file changed, 5 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index a2a953693b45..f9b9b3aefc4a 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -314,6 +314,7 @@ static void drm_sched_job_timedout(struct work_struct *work)
>  {
>         struct drm_gpu_scheduler *sched;
>         struct drm_sched_job *job;
> +       struct dma_fence *fence;
>         enum drm_gpu_sched_stat status = DRM_GPU_SCHED_STAT_NOMINAL;
>
>         sched = container_of(work, struct drm_gpu_scheduler, work_tdr.work);
> @@ -325,11 +326,10 @@ static void drm_sched_job_timedout(struct work_struct *work)
>
>         if (job) {
>                 /*
> -                * Remove the bad job so it cannot be freed by concurrent
> -                * drm_sched_cleanup_jobs. It will be reinserted back after sched->thread
> -                * is parked at which point it's safe.
> +                * Get job->s_fence->parent here to avoid concurrent delete during
> +                * processing timedout_job
>                  */
> -               list_del_init(&job->list);
> +               fence = dma_fence_get(job->s_fence->parent);
>                 spin_unlock(&sched->job_list_lock);
>
>                 status = job->sched->ops->timedout_job(job);
> @@ -342,6 +342,7 @@ static void drm_sched_job_timedout(struct work_struct *work)
>                         job->sched->ops->free_job(job);
>                         sched->free_guilty = false;
>                 }
> +               dma_fence_put(fence);
>         } else {
>                 spin_unlock(&sched->job_list_lock);
>         }
> @@ -392,20 +393,6 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
>
>         kthread_park(sched->thread);
>
> -       /*
> -        * Reinsert back the bad job here - now it's safe as
> -        * drm_sched_get_cleanup_job cannot race against us and release the
> -        * bad job at this point - we parked (waited for) any in progress
> -        * (earlier) cleanups and drm_sched_get_cleanup_job will not be called
> -        * now until the scheduler thread is unparked.
> -        */
> -       if (bad && bad->sched == sched)
> -               /*
> -                * Add at the head of the queue to reflect it was the earliest
> -                * job extracted.
> -                */
> -               list_add(&bad->list, &sched->pending_list);
> -
>         /*
>          * Iterate the job list from later to  earlier one and either deactive
>          * their HW callbacks or remove them from pending list if they already
> --
> 2.25.1
>