On Wed, Jul 10, 2024 at 02:40:04PM +0200, Christian König wrote: > Am 10.07.24 um 13:58 schrieb Daniel Vetter: > > On Wed, 10 Jul 2024 at 13:39, Christian König <christian.koenig@xxxxxxx> wrote: > > > 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. > > You're not allowed to take a fault under dma_resv, because drivers > > might need to take that lock to handle faults. So unfortunately in our > > combined lockdep priming, there really seems to be no chain yet that > > teaches about faults possibly happening while holding > > drm_modeset_lock. > > Ah, of course! You are right, it was just the other way around. Applied to drm-misc-next, thanks for your review. -Sima > > Thanks, > Christian. > > > -Sima > > > > > > 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) > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
