From: Daniel Vetter <daniel@ffwll.ch>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
Boqun Feng <boqun.feng@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Cc: tzimmermann@suse.de, airlied@linux.ie,
gregkh@linuxfoundation.org, intel-gfx@lists.freedesktop.org,
linux-kernel@vger.kernel.org, mripard@kernel.org,
Daniel Vetter <daniel.vetter@ffwll.ch>,
linux-graphics-maintainer@vmware.com,
dri-devel@lists.freedesktop.org, skhan@linuxfoundation.org,
linux-kernel-mentees@lists.linuxfoundation.org, zackr@vmware.com
Subject: Re: [Intel-gfx] [PATCH 1/3] drm: use the lookup lock in drm_is_current_master
Date: Thu, 22 Jul 2021 12:38:10 +0200 [thread overview]
Message-ID: <YPlKkvelm/mcnCj0@phenom.ffwll.local> (raw)
In-Reply-To: <20210722092929.244629-2-desmondcheongzx@gmail.com>
On Thu, Jul 22, 2021 at 05:29:27PM +0800, Desmond Cheong Zhi Xi wrote:
> Inside drm_is_current_master, using the outer drm_device.master_mutex
> to protect reads of drm_file.master makes the function prone to creating
> lock hierarchy inversions. Instead, we can use the
> drm_file.master_lookup_lock that sits at the bottom of the lock
> hierarchy.
>
> Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> ---
> drivers/gpu/drm/drm_auth.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
> index f00354bec3fb..9c24b8cc8e36 100644
> --- a/drivers/gpu/drm/drm_auth.c
> +++ b/drivers/gpu/drm/drm_auth.c
> @@ -63,8 +63,9 @@
>
> static bool drm_is_current_master_locked(struct drm_file *fpriv)
> {
> - lockdep_assert_held_once(&fpriv->minor->dev->master_mutex);
> -
> + /* Either drm_device.master_mutex or drm_file.master_lookup_lock
> + * should be held here.
> + */
Disappointing that lockdep can't check or conditions for us, a
lockdep_assert_held_either would be really neat in some cases.
Adding lockdep folks, maybe they have ideas.
On the patch:
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
> }
>
> @@ -82,9 +83,9 @@ bool drm_is_current_master(struct drm_file *fpriv)
> {
> bool ret;
>
> - mutex_lock(&fpriv->minor->dev->master_mutex);
> + spin_lock(&fpriv->master_lookup_lock);
> ret = drm_is_current_master_locked(fpriv);
> - mutex_unlock(&fpriv->minor->dev->master_mutex);
> + spin_unlock(&fpriv->master_lookup_lock);
>
> return ret;
> }
> --
> 2.25.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
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next prev parent reply other threads:[~2021-07-22 10:38 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-22 9:29 [Intel-gfx] [PATCH 0/3] drm, drm/vmwgfx: fixes and updates related to drm_master Desmond Cheong Zhi Xi
2021-07-22 9:29 ` [Intel-gfx] [PATCH 1/3] drm: use the lookup lock in drm_is_current_master Desmond Cheong Zhi Xi
2021-07-22 10:38 ` Daniel Vetter [this message]
2021-07-22 15:04 ` Boqun Feng
2021-07-22 19:02 ` Daniel Vetter
2021-07-23 7:16 ` Boqun Feng
2021-07-27 14:37 ` Peter Zijlstra
2021-07-29 7:00 ` Daniel Vetter
2021-07-29 14:32 ` Desmond Cheong Zhi Xi
2021-07-29 14:45 ` Peter Zijlstra
2021-07-22 9:29 ` [Intel-gfx] [PATCH 2/3] drm: clarify lifetime/locking for drm_master's lease fields Desmond Cheong Zhi Xi
2021-07-22 10:35 ` Daniel Vetter
2021-07-22 13:02 ` Desmond Cheong Zhi Xi
2021-07-22 14:17 ` Daniel Vetter
2021-07-22 9:29 ` [Intel-gfx] [PATCH 3/3] drm/vmwgfx: fix potential UAF in vmwgfx_surface.c Desmond Cheong Zhi Xi
2021-07-22 10:39 ` Daniel Vetter
2021-07-22 19:17 ` Zack Rusin
2021-07-23 6:44 ` Desmond Cheong Zhi Xi
2021-07-22 14:05 ` [Intel-gfx] ✗ Fi.CI.SPARSE: warning for drm, drm/vmwgfx: fixes and updates related to drm_master Patchwork
2021-07-22 14:34 ` [Intel-gfx] ✗ Fi.CI.BAT: failure " Patchwork
2021-07-27 17:42 ` [Intel-gfx] ✗ Fi.CI.BUILD: failure for drm, drm/vmwgfx: fixes and updates related to drm_master (rev2) Patchwork
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