linux-kernel - [PATCH] drm/syncobj: make lockdep complain on WAIT_FOR

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Message-Id: <20210118180334.43714-2-christian.koenig@amd.com>
Date:   Mon, 18 Jan 2021 19:03:34 +0100
From:   "Christian König" 
        <ckoenig.leichtzumerken@...il.com>
To:     daniel@...ll.ch, peterz@...radead.org, mingo@...hat.com,
        will@...nel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] drm/syncobj: make lockdep complain on WAIT_FOR_SUBMIT v2

DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT can't be used when we hold locks
since we are basically waiting for userspace to do something.

Holding a lock while doing so can trivial deadlock with page faults
etc...

So make lockdep complain when a driver tries to do this.

v2: Add lockdep_assert_none_held() macro.

Signed-off-by: Christian König <christian.koenig@....com>
---
 drivers/gpu/drm/drm_syncobj.c | 7 +++++++
 include/linux/lockdep.h       | 5 +++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 6e74e6745eca..f51458615158 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -387,6 +387,13 @@ int drm_syncobj_find_fence(struct drm_file *file_private,
 	if (!syncobj)
 		return -ENOENT;
 
+	/* Waiting for userspace with locks help is illegal cause that can
+	 * trivial deadlock with page faults for example. Make lockdep complain
+	 * about it early on.
+	 */
+	if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT)
+		lockdep_assert_none_held_once();
+
 	*fence = drm_syncobj_fence_get(syncobj);
 	drm_syncobj_put(syncobj);
 
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..6eb117c0d0f3 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -310,6 +310,10 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
 		WARN_ON_ONCE(debug_locks && !lockdep_is_held(l));	\
 	} while (0)
 
+#define lockdep_assert_none_held_once()	do {				\
+		WARN_ON_ONCE(debug_locks && current->lockdep_depth);	\
+	} while (0)
+
 #define lockdep_recursing(tsk)	((tsk)->lockdep_recursion)
 
 #define lockdep_pin_lock(l)	lock_pin_lock(&(l)->dep_map)
@@ -387,6 +391,7 @@ extern int lockdep_is_held(const void *);
 #define lockdep_assert_held_write(l)	do { (void)(l); } while (0)
 #define lockdep_assert_held_read(l)		do { (void)(l); } while (0)
 #define lockdep_assert_held_once(l)		do { (void)(l); } while (0)
+#define lockdep_assert_none_held_once()	do { } while (0)
 
 #define lockdep_recursing(tsk)			(0)
 
-- 
2.25.1