Am 10.07.24 um 11:31 schrieb Daniel Vetter:
We already teach lockdep that dma_resv nests within drm_modeset_lock,
but there's a lot more: All drm kms ioctl rely on being able to
put/get_user while holding modeset locks, so we really need a
might_fault in there too to complete the picture. Add it.
Mhm, lockdep should be able to deduce that when there might be faults
under the dma_resv lock there might also be faults under the
drm_modeset_lock.
Motivated by a syzbot report that blew up on bcachefs doing an
unconditional console_lock way deep in the locking hierarchy, and
lockdep only noticing the depency loop in a drm ioctl instead of much
earlier. This annotation will make sure such issues have a much harder
time escaping.
References: https://lore.kernel.org/dri-devel/00000000000073db8b061cd43496@xxxxxxxxxx/
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: "Christian König" <christian.koenig@xxxxxxx>
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
On the other hand pointing it out explicitly doesn't hurts us at all, so
Reviewed-by: Christian König <christian.koenig@xxxxxxx>.
Regards,
Christian.
---
drivers/gpu/drm/drm_mode_config.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 568972258222..37d2e0a4ef4b 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -456,6 +456,8 @@ int drmm_mode_config_init(struct drm_device *dev)
if (ret == -EDEADLK)
ret = drm_modeset_backoff(&modeset_ctx);
+ might_fault();
+
ww_acquire_init(&resv_ctx, &reservation_ww_class);
ret = dma_resv_lock(&resv, &resv_ctx);
if (ret == -EDEADLK)
