drm/syncobj: make lockdep complain on WAIT_FOR_SUBMIT v3

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.
v3: Add might_sleep() and also use lockdep_assert_none_held() in the
    IOCTL path.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patchwork.freedesktop.org/patch/414944/

drivers/gpu/drm/drm_syncobj.c

@@ -387,6 +387,15 @@ 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) {
+		might_sleep();
+		lockdep_assert_none_held_once();
+	}
+
 	*fence = drm_syncobj_fence_get(syncobj);
 	drm_syncobj_put(syncobj);
 
@@ -940,6 +949,9 @@ static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,
 	uint64_t *points;
 	uint32_t signaled_count, i;
 
+	if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT)
+		lockdep_assert_none_held_once();
+
 	points = kmalloc_array(count, sizeof(*points), GFP_KERNEL);
 	if (points == NULL)
 		return -ENOMEM;

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)