On 02/08/2016 02:13 AM, Mario Kleiner wrote: > Changes to drm_update_vblank_count() in Linux 4.4 broke the > behaviour of the pre/post modeset functions as the new update > code doesn't deal with hw vblank counter resets inbetween calls > to drm_vblank_pre_modeset an drm_vblank_post_modeset, as it > should. > > This causes mistreatment of such hw counter resets as counter > wraparound, and thereby large forward jumps of the software > vblank counter which in turn cause vblank event dispatching > and vblank waits to fail/hang --> userspace clients hang. > > This symptom was reported on radeon-kms to cause a infinite > hang of KDE Plasma 5 shell's login procedure, preventing users > from logging in. > > Fix this by detecting when drm_update_vblank_count() is called > inside a pre->post modeset interval. If so, clamp valid vblank > increments to the safe values 0 and 1, pretty much restoring > the update behavior of the old update code of Linux 4.3 and > earlier. Also reset the last recorded hw vblank count at call > to drm_vblank_post_modeset() to be safe against hw that after > modesetting, dpms on etc. only fires its first vblank irq after > drm_vblank_post_modeset() was already called. > > Reported-by: Vlastimil Babka <vbabka at suse.cz>
FWIW, I've applied the whole patchset to 4.4 and the kde5 login problem didn't occur. I can test the next version too. Thanks, Vlastimil
