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From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: linux-graphics-maintainer@vmware.com, zackr@vmware.com,
	airlied@linux.ie, daniel@ffwll.ch,
	maarten.lankhorst@linux.intel.com, mripard@kernel.org,
	tzimmermann@suse.de, corbet@lwn.net
Cc: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	skhan@linuxfoundation.org, gregkh@linuxfoundation.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	intel-gfx@lists.freedesktop.org,
	Daniel Vetter <daniel.vetter@ffwll.ch>
Subject: [PATCH v2 1/3] drm: use the lookup lock in drm_is_current_master
Date: Sat, 24 Jul 2021 19:18:22 +0800	[thread overview]
Message-ID: <20210724111824.59266-2-desmondcheongzx@gmail.com> (raw)
In-Reply-To: <20210724111824.59266-1-desmondcheongzx@gmail.com>

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>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 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.
+	 */
 	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


  reply	other threads:[~2021-07-24 11:19 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-24 11:18 [PATCH v2 0/3] drm, drm/vmwgfx: fixes and updates related to drm_master Desmond Cheong Zhi Xi
2021-07-24 11:18 ` Desmond Cheong Zhi Xi [this message]
2021-07-27 13:04   ` [PATCH v2 1/3] drm: use the lookup lock in drm_is_current_master Daniel Vetter
2021-07-24 11:18 ` [PATCH v2 2/3] drm: clarify usage of drm leases Desmond Cheong Zhi Xi
2021-07-27 13:04   ` Daniel Vetter
2021-07-28 10:01     ` Desmond Cheong Zhi Xi
2021-07-24 11:18 ` [PATCH v2 3/3] drm/vmwgfx: fix potential UAF in vmwgfx_surface.c Desmond Cheong Zhi Xi

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