linux-kernel - Re: [PATCH] drm/i915: Move fd_install after last use of fence

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Date:   Fri, 3 Feb 2023 10:15:56 -0800
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Rob Clark <robdclark@...omium.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Matthew Auld <matthew.auld@...el.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Niranjana Vishwanathapura <niranjana.vishwanathapura@...el.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Nirmoy Das <nirmoy.das@...el.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>,
        intel-gfx@...ts.freedesktop.org,
        open list <linux-kernel@...r.kernel.org>,
        jason.ekstrand@...labora.com
Subject: Re: [PATCH] drm/i915: Move fd_install after last use of fence

On Fri, Feb 3, 2023 at 8:49 AM Rob Clark <robdclark@...il.com> wrote:
>
> From: Rob Clark <robdclark@...omium.org>
>
> Because eb_composite_fence_create() drops the fence_array reference
> after creation of the sync_file, only the sync_file holds a ref to the
> fence.  But fd_install() makes that reference visable to userspace, so
> it must be the last thing we do with the fence.
>

Fixes: 00dae4d3d35d ("drm/i915: Implement SINGLE_TIMELINE with a syncobj (v4)")

> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index f266b68cf012..0f2e056c02dd 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -3476,38 +3476,38 @@ i915_gem_do_execbuffer(struct drm_device *dev,
>
>  err_request:
>         eb_requests_get(&eb);
>         err = eb_requests_add(&eb, err);
>
>         if (eb.fences)
>                 signal_fence_array(&eb, eb.composite_fence ?
>                                    eb.composite_fence :
>                                    &eb.requests[0]->fence);
>
> +       if (unlikely(eb.gem_context->syncobj)) {
> +               drm_syncobj_replace_fence(eb.gem_context->syncobj,
> +                                         eb.composite_fence ?
> +                                         eb.composite_fence :
> +                                         &eb.requests[0]->fence);
> +       }
> +
>         if (out_fence) {
>                 if (err == 0) {
>                         fd_install(out_fence_fd, out_fence->file);
>                         args->rsvd2 &= GENMASK_ULL(31, 0); /* keep in-fence */
>                         args->rsvd2 |= (u64)out_fence_fd << 32;
>                         out_fence_fd = -1;
>                 } else {
>                         fput(out_fence->file);
>                 }
>         }
>
> -       if (unlikely(eb.gem_context->syncobj)) {
> -               drm_syncobj_replace_fence(eb.gem_context->syncobj,
> -                                         eb.composite_fence ?
> -                                         eb.composite_fence :
> -                                         &eb.requests[0]->fence);
> -       }
> -
>         if (!out_fence && eb.composite_fence)
>                 dma_fence_put(eb.composite_fence);
>
>         eb_requests_put(&eb);
>
>  err_vma:
>         eb_release_vmas(&eb, true);
>         WARN_ON(err == -EDEADLK);
>         i915_gem_ww_ctx_fini(&eb.ww);
>
> --
> 2.38.1
>