On Tue, Jan 19, 2021 at 12:48 PM Christian König ckoenig.leichtzumerken@gmail.com wrote:

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

drivers/gpu/drm/drm_syncobj.c | 12 ++++++++++++ include/linux/lockdep.h | 5 +++++ 2 files changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c index 6e74e6745eca..9ecfec1e5567 100644 --- a/drivers/gpu/drm/drm_syncobj.c +++ b/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);
  

I noticed a use-after-free here that goes back to 5.2, sending out a patch for that.

@@ -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;
  

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)

ofc needs ack from Peter, but drm parts look all good to me.

Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch

-- 2.25.1

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