@@ -1743,7 +1743,9 @@ EXPORT_SYMBOL(drm_atomic_helper_wait_for_flip_done);
void drm_atomic_helper_commit_tail(struct drm_atomic_state *old_state)
{
struct drm_device *dev = old_state->dev;
+ static DEFINE_MUTEX(lock);
+ mutex_lock(&lock);
drm_atomic_helper_commit_modeset_disables(dev, old_state);
drm_atomic_helper_commit_planes(dev, old_state, 0);
@@ -1757,6 +1759,7 @@ void drm_atomic_helper_commit_tail(struct drm_atomic_state *old_state)
drm_atomic_helper_wait_for_vblanks(dev, old_state);
drm_atomic_helper_cleanup_planes(dev, old_state);
+ mutex_unlock(&lock);
}
EXPORT_SYMBOL(drm_atomic_helper_commit_tail);
To briefly summarize the issues reported by syzbot, there are two task call stacks as follows: Task A Task B ------------------------------------ ---------------------------------- drm_atomic_commit drm_atomic_helper_commit commit_work commit_tail drm_atomic_helper_commit_tail commit_tail drm_atomic_helper_commit_tail drm_client_modeset_commit_atomic drm_atomic_state_default_clear drm_atomic_helper_wait_for_vblanks When two prerequisites are met simultaneously, the current issue will be triggered: 1. There is an overlap in the memory range occupied by the crtcs member set contained in the instance state of "struct drm_atomic_state" created by Task A and Task B 2. The context of drm_atomic_helper_commit_tail() has no lock protection, resulting in the instance state->crtcs sub item being released by other task The solution is to add a lock in drm_atomic_helper_commit_tail() to ensure that there is no other task interference when accessing the instance state. Reported-and-tested-by: syzbot+0f999d26a4fd79c3a23b@syzkaller.appspotmail.com Signed-off-by: Edward Adam Davis <eadavis@qq.com> --- drivers/gpu/drm/drm_atomic_helper.c | 3 +++ 1 file changed, 3 insertions(+)