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/00000000000073db8b061cd43...@google.com/ Signed-off-by: Daniel Vetter <daniel.vet...@intel.com> Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com> Cc: Maxime Ripard <mrip...@kernel.org> Cc: Thomas Zimmermann <tzimmerm...@suse.de> Cc: Sumit Semwal <sumit.sem...@linaro.org> Cc: "Christian König" <christian.koe...@amd.com> Cc: linux-me...@vger.kernel.org Cc: linaro-mm-...@lists.linaro.org
On the other hand pointing it out explicitly doesn't hurts us at all, so Reviewed-by: Christian König <christian.koe...@amd.com>.
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)
