[Intel-gfx] [PATCH v5 02/20] drm/msm: Fix drm/sched point of no return rules

[Rob Clark]

On Thu, Aug 5, 2021 at 3:47 AM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> Originally drm_sched_job_init was the point of no return, after which
> drivers must submit a job. I've split that up, which allows us to fix
> this issue pretty easily.
>
> Only thing we have to take care of is to not skip to error paths after
> that. Other drivers do this the same for out-fence and similar things.
>
> Fixes: 1d8a5ca436ee ("drm/msm: Conversion to drm scheduler")
> Cc: Rob Clark <robdclark at chromium.org>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Sean Paul <sean at poorly.run>
> Cc: Sumit Semwal <sumit.semwal at linaro.org>
> Cc: "Christian König" <christian.koenig at amd.com>
> Cc: linux-arm-msm at vger.kernel.org
> Cc: dri-devel at lists.freedesktop.org
> Cc: freedreno at lists.freedesktop.org
> Cc: linux-media at vger.kernel.org
> Cc: linaro-mm-sig at lists.linaro.org
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
>  drivers/gpu/drm/msm/msm_gem_submit.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> index 6d6c44f0e1f3..d0ed4ddc509e 100644
> --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> @@ -52,9 +52,6 @@ static struct msm_gem_submit *submit_create(struct drm_device *dev,
>                 return ERR_PTR(ret);
>         }
>
> -       /* FIXME: this is way too early */
> -       drm_sched_job_arm(&job->base);
> -
>         xa_init_flags(&submit->deps, XA_FLAGS_ALLOC);
>
>         kref_init(&submit->ref);
> @@ -883,6 +880,9 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
>
>         submit->user_fence = dma_fence_get(&submit->base.s_fence->finished);
>
> +       /* point of no return, we _have_ to submit no matter what */
> +       drm_sched_job_arm(&submit->base);
> +
>         /*
>          * Allocate an id which can be used by WAIT_FENCE ioctl to map back
>          * to the underlying fence.
> @@ -892,17 +892,16 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
>         if (submit->fence_id < 0) {
>                 ret = submit->fence_id = 0;
>                 submit->fence_id = 0;
> -               goto out;
>         }
>
> -       if (args->flags & MSM_SUBMIT_FENCE_FD_OUT) {
> +       if (ret == 0 && args->flags & MSM_SUBMIT_FENCE_FD_OUT) {
>                 struct sync_file *sync_file = sync_file_create(submit->user_fence);
>                 if (!sync_file) {
>                         ret = -ENOMEM;
> -                       goto out;
> +               } else {
> +                       fd_install(out_fence_fd, sync_file->file);
> +                       args->fence_fd = out_fence_fd;
>                 }
> -               fd_install(out_fence_fd, sync_file->file);
> -               args->fence_fd = out_fence_fd;

I wonder if instead we should (approximately) undo "drm/msm/submit:
Simplify out-fence-fd handling" so that the point that it could fail
is moved up ahead of the drm_sched_job_arm()?

Also, does the dma_fence_get() work before drm_sched_job_arm()?  From
a quick look, it looks like it won't, but I'm still playing catchup
and haven't had a chance to look at your entire series.  If it doesn't
work before drm_sched_job_arm(), then there is really no way to
prevent a error path between the fence-init and job-submit.

But, prior to your series, wouldn't a failure after
drm_sched_job_init() but before the job is submitted just burn a
fence-id, and otherwise carry on it's merry way?

BR,
-R

>         }
>
>         submit_attach_object_fences(submit);
> --
> 2.32.0
>