linux-kernel - Re: [Freedreno] [PATCH] drm/msm/gem: Unpin objects slightly later

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Date:   Thu, 29 Sep 2022 13:04:40 -0700
From:   Chia-I Wu <olvaffe@...il.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        David Airlie <airlied@...ux.ie>, linux-arm-msm@...r.kernel.org,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        open list <linux-kernel@...r.kernel.org>,
        Sean Paul <sean@...rly.run>, Daniel Vetter <daniel@...ll.ch>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        freedreno@...ts.freedesktop.org
Subject: Re: [Freedreno] [PATCH] drm/msm/gem: Unpin objects slightly later

On Fri, Sep 23, 2022 at 3:41 PM Rob Clark <robdclark@...il.com> wrote:
>
> From: Rob Clark <robdclark@...omium.org>
>
> The introduction of 025d27239a2f exposes a problem with f371bcc0c2ac, in
> that we need to keep the object pinned in the time the submit is queued
> up in the gpu scheduler.  Otherwise the shrinker will see it as a thing
> that can be evicted if we wait for it to be signaled.  But if the
> shrinker path is waiting on it with the obj lock held, the job cannot be
> scheduled, as that also requires briefly grabbing the obj lock, leading
> to deadlock.  (Not to mention, we don't want the shrinker to evict an
> obj queued up in gpu scheduler.)
>
> Fixes: f371bcc0c2ac ("drm/msm/gem: Unpin buffers earlier")
> Fixes: 025d27239a2f ("drm/msm/gem: Evict active GEM objects when necessary")
> Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/19
> Signed-off-by: Rob Clark <robdclark@...omium.org>
Tested-by: Chia-I Wu <olvaffe@...il.com>
> ---
>  drivers/gpu/drm/msm/msm_gem_submit.c | 4 ++--
>  drivers/gpu/drm/msm/msm_ringbuffer.c | 3 ++-
>  2 files changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> index 5599d93ec0d2..c670591995e6 100644
> --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> @@ -501,11 +501,11 @@ static int submit_reloc(struct msm_gem_submit *submit, struct msm_gem_object *ob
>   */
>  static void submit_cleanup(struct msm_gem_submit *submit, bool error)
>  {
> -       unsigned cleanup_flags = BO_LOCKED | BO_OBJ_PINNED;
> +       unsigned cleanup_flags = BO_LOCKED;
>         unsigned i;
>
>         if (error)
> -               cleanup_flags |= BO_VMA_PINNED;
> +               cleanup_flags |= BO_VMA_PINNED | BO_OBJ_PINNED;
>
>         for (i = 0; i < submit->nr_bos; i++) {
>                 struct msm_gem_object *msm_obj = submit->bos[i].obj;
> diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.c b/drivers/gpu/drm/msm/msm_ringbuffer.c
> index cad4c3525f0b..57a8e9564540 100644
> --- a/drivers/gpu/drm/msm/msm_ringbuffer.c
> +++ b/drivers/gpu/drm/msm/msm_ringbuffer.c
> @@ -25,7 +25,8 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
>
>                 msm_gem_lock(obj);
>                 msm_gem_unpin_vma_fenced(submit->bos[i].vma, fctx);
> -               submit->bos[i].flags &= ~BO_VMA_PINNED;
> +               msm_gem_unpin_locked(obj);
> +               submit->bos[i].flags &= ~(BO_VMA_PINNED | BO_OBJ_PINNED);
>                 msm_gem_unlock(obj);
>         }
>
> --
> 2.37.2
>