[RESEND PATCH v2 0/2] locking/lockdep, drm: apply new lockdep assert in drm_auth.c

[RESEND PATCH v2 0/2] locking/lockdep, drm: apply new lockdep assert in drm_auth.c

[Desmond Cheong Zhi Xi]

Hi all,

My bad for the resend. Adding cc: intel-gfx, and the maintainers and
mailing lists for include/drm/drm_file.h.

Following a discussion on the patch ("drm: use the lookup lock in
drm_is_current_master") [1], Peter Zijlstra proposed new lockdep_assert
helpers to make it convenient to compose lockdep checks together.

This series includes the patch that introduces the new lockdep helpers,
then utilizes these helpers in drm_is_current_master_locked in the
following patch.

v1 -> v2:
Patch 2:
- Updated the kerneldoc on the lock design of drm_file.master to explain
the use of lockdep_assert(). As suggested by Boqun Feng.

Link: https://lore.kernel.org/lkml/20210722092929.244629-2-desmondcheongzx@gmail.com/ [1]

Best wishes,
Desmond

Desmond Cheong Zhi Xi (1):
  drm: add lockdep assert to drm_is_current_master_locked

Peter Zijlstra (1):
  locking/lockdep: Provide lockdep_assert{,_once}() helpers

 drivers/gpu/drm/drm_auth.c |  6 +++---
 include/drm/drm_file.h     |  4 ++++
 include/linux/lockdep.h    | 41 +++++++++++++++++++-------------------
 3 files changed, 28 insertions(+), 23 deletions(-)

-- 
2.25.1

[RESEND PATCH v2 1/2] locking/lockdep: Provide lockdep_assert{,_once}() helpers

[Desmond Cheong Zhi Xi]

From: Peter Zijlstra <peterz@infradead.org>

Extract lockdep_assert{,_once}() helpers to more easily write composite
assertions like, for example:

	lockdep_assert(lockdep_is_held(&drm_device.master_mutex) ||
		       lockdep_is_held(&drm_file.master_lookup_lock));

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 include/linux/lockdep.h | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 5cf387813754..9fe165beb0f9 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -306,31 +306,29 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
 
 #define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
 
-#define lockdep_assert_held(l)	do {					\
-		WARN_ON(debug_locks &&					\
-			lockdep_is_held(l) == LOCK_STATE_NOT_HELD);	\
-	} while (0)
+#define lockdep_assert(cond)		\
+	do { WARN_ON(debug_locks && !(cond)); } while (0)
 
-#define lockdep_assert_not_held(l)	do {				\
-		WARN_ON(debug_locks &&					\
-			lockdep_is_held(l) == LOCK_STATE_HELD);		\
-	} while (0)
+#define lockdep_assert_once(cond)	\
+	do { WARN_ON_ONCE(debug_locks && !(cond)); } while (0)
 
-#define lockdep_assert_held_write(l)	do {			\
-		WARN_ON(debug_locks && !lockdep_is_held_type(l, 0));	\
-	} while (0)
+#define lockdep_assert_held(l)		\
+	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
 
-#define lockdep_assert_held_read(l)	do {				\
-		WARN_ON(debug_locks && !lockdep_is_held_type(l, 1));	\
-	} while (0)
+#define lockdep_assert_not_held(l)	\
+	lockdep_assert(lockdep_is_held(l) != LOCK_STATE_HELD)
 
-#define lockdep_assert_held_once(l)	do {				\
-		WARN_ON_ONCE(debug_locks && !lockdep_is_held(l));	\
-	} while (0)
+#define lockdep_assert_held_write(l)	\
+	lockdep_assert(lockdep_is_held_type(l, 0))
 
-#define lockdep_assert_none_held_once()	do {				\
-		WARN_ON_ONCE(debug_locks && current->lockdep_depth);	\
-	} while (0)
+#define lockdep_assert_held_read(l)	\
+	lockdep_assert(lockdep_is_held_type(l, 1))
+
+#define lockdep_assert_held_once(l)		\
+	lockdep_assert_once(lockdep_is_held(l) != LOCK_STATE_NOT_HELD)
+
+#define lockdep_assert_none_held_once()		\
+	lockdep_assert_once(!current->lockdep_depth)
 
 #define lockdep_recursing(tsk)	((tsk)->lockdep_recursion)
 
@@ -407,6 +405,9 @@ extern int lock_is_held(const void *);
 extern int lockdep_is_held(const void *);
 #define lockdep_is_held_type(l, r)		(1)
 
+#define lockdep_assert(c)			do { } while (0)
+#define lockdep_assert_once(c)			do { } while (0)
+
 #define lockdep_assert_held(l)			do { (void)(l); } while (0)
 #define lockdep_assert_not_held(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held_write(l)		do { (void)(l); } while (0)
-- 
2.25.1

[RESEND PATCH v2 2/2] drm: add lockdep assert to drm_is_current_master_locked

[Desmond Cheong Zhi Xi]

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>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 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

Re: [RESEND PATCH v2 2/2] drm: add lockdep assert to drm_is_current_master_locked

[Daniel Vetter]

On Mon, Aug 02, 2021 at 06:59:57PM +0800, Desmond Cheong Zhi Xi wrote:
> 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>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Both patches pushed to drm-misc-next, thanks.
-Daniel

> ---
>  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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch