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From: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To: maarten.lankhorst@linux.intel.com, mripard@kernel.org,
	tzimmermann@suse.de, airlied@linux.ie, daniel@ffwll.ch,
	peterz@infradead.org, mingo@redhat.com, will@kernel.org,
	longman@redhat.com, boqun.feng@gmail.com
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
Subject: [PATCH v2 2/2] drm: add lockdep assert to drm_is_current_master_locked
Date: Sat, 31 Jul 2021 16:24:58 +0800	[thread overview]
Message-ID: <20210731082458.1962043-3-desmondcheongzx@gmail.com> (raw)
In-Reply-To: <20210731082458.1962043-1-desmondcheongzx@gmail.com>

In drm_is_current_master_locked, accessing drm_file.master should be
protected by either drm_file.master_lookup_lock or
drm_device.master_mutex. This was previously awkward to assert with
lockdep.

Following patch ("locking/lockdep: Provide lockdep_assert{,_once}()
helpers"), this assertion is now convenient. So we add in the
assertion and explain this lock design in the kerneldoc.

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Waiman Long <longman@redhat.com>
---
 drivers/gpu/drm/drm_auth.c | 6 +++---
 include/drm/drm_file.h     | 4 ++++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 9c24b8cc8e36..6f4d7ff23c80 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -63,9 +63,9 @@
 
 static bool drm_is_current_master_locked(struct drm_file *fpriv)
 {
-	/* Either drm_device.master_mutex or drm_file.master_lookup_lock
-	 * should be held here.
-	 */
+	lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) ||
+			    lockdep_is_held(&fpriv->minor->dev->master_mutex));
+
 	return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
 }
 
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 726cfe0ff5f5..a3acb7ac3550 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -233,6 +233,10 @@ struct drm_file {
 	 * this only matches &drm_device.master if the master is the currently
 	 * active one.
 	 *
+	 * To update @master, both &drm_device.master_mutex and
+	 * @master_lookup_lock need to be held, therefore holding either of
+	 * them is safe and enough for the read side.
+	 *
 	 * When dereferencing this pointer, either hold struct
 	 * &drm_device.master_mutex for the duration of the pointer's use, or
 	 * use drm_file_get_master() if struct &drm_device.master_mutex is not
-- 
2.25.1


  parent reply	other threads:[~2021-07-31  8:27 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-31  8:24 [PATCH v2 0/2] locking/lockdep, drm: apply new lockdep assert in drm_auth.c Desmond Cheong Zhi Xi
2021-07-31  8:24 ` [PATCH v2 1/2] locking/lockdep: Provide lockdep_assert{,_once}() helpers Desmond Cheong Zhi Xi
2021-08-02  9:49   ` Maarten Lankhorst
2021-07-31  8:24 ` Desmond Cheong Zhi Xi [this message]
2021-08-02  8:26 ` [PATCH v2 0/2] locking/lockdep, drm: apply new lockdep assert in drm_auth.c Daniel Vetter
2021-08-02  9:42   ` Peter Zijlstra
2021-08-02 10:44   ` Desmond Cheong Zhi Xi

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