The changes to drm_update_vblank_count() in Linux 4.4 added a method to emulate a hardware vblank counter by use of high precision vblank timestamps if a kms driver supports those, but doesn't suppport hw vblank counters. That method assumes that the old timestamp from a previous invocation is valid, but that is not always the case. E.g., if drm_reset_vblank_timestamp() gets called during drm_vblank_on() or drm_update_vblank_count() gets called outside vblank irq and the high precision timestamping can't deliver a precise timestamp, ie. drm_get_last_vbltimestamp() delivers a return value of false, then those functions will initialize the old timestamp to zero to mark it as invalid. A following call to drm_update_vblank_count() would then calculate elapsed time with vblank irqs off as current vblank timestamp minus the zero old timestamp and compute a software vblank counter increment that corresponds to system uptime, causing a large forward jump of the software vblank counter. That jump in turn can cause too long waits in drmWaitVblank and very long delays in delivery of vblank events, resulting in hangs of userspace clients. This problem can be observed on nouveau-kms during machine suspend->resume cycles, where drm_vblank_off is called during suspend, drm_vblank_on is called during resume and the first queries to drm_get_last_vbltimestamp() don't deliver high precision timestamps, resulting in a large harmful counter jump. Fix this by checking if the old timestamp used for this calculations is zero == invalid. If so, perform a counter increment of +1 to prevent large counter jumps and reinitialize the timestamps to sane values. Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 4.4+ Cc: michel@xxxxxxxxxxx Cc: vbabka@xxxxxxx Cc: ville.syrjala@xxxxxxxxxxxxxxx Cc: daniel.vetter@xxxxxxxx Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx Cc: alexander.deucher@xxxxxxx Cc: christian.koenig@xxxxxxx --- drivers/gpu/drm/drm_irq.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index fb17c45..88bdf19 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -216,6 +216,13 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe, DRM_DEBUG_VBL("crtc %u: Redundant vblirq ignored." " diff_ns = %lld, framedur_ns = %d)\n", pipe, (long long) diff_ns, framedur_ns); + + /* No valid t_old to calculate diff? Bump +1 to force reinit. */ + if (t_old->tv_sec == 0 && t_old->tv_usec == 0) { + DRM_DEBUG_VBL("crtc %u: No baseline ts. Bump +1.\n", + pipe); + diff = 1; + } } else { /* some kind of default for drivers w/o accurate vbl timestamping */ diff = (flags & DRM_CALLED_FROM_VBLIRQ) != 0; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html