On Wed, Oct 01, 2025 at 07:57:23PM -0700, Chintan Patel wrote: > When wait_event_timeout() in drm_wait_one_vblank() times out, the > current WARN can cause unnecessary kernel panics in environments > with panic_on_warn set (e.g. CI, fuzzing). These timeouts can happen > under scheduler pressure or from invalid userspace calls, so they are > not always a kernel bug.
"invalid userspace calls" should never reach this far. That would be a kernel bug. > > Replace the WARN with drm_dbg_kms() messages that provide useful > context (last and current vblank counters) without crashing the > system. Developers can still enable drm.debug to diagnose genuine > problems. > > Reported-by: syzbot+147ba789658184f0c...@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=147ba789658184f0ce04 > Tested-by: syzbot+147ba789658184f0c...@syzkaller.appspotmail.com > > Signed-off-by: Chintan Patel <chintanl...@gmail.com> > > v2: > - Drop unnecessary in-code comment (suggested by Thomas Zimmermann) > - Remove else branch, only log timeout case > --- > drivers/gpu/drm/drm_vblank.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c > index 46f59883183d..a94570668cba 100644 > --- a/drivers/gpu/drm/drm_vblank.c > +++ b/drivers/gpu/drm/drm_vblank.c > @@ -1289,7 +1289,7 @@ void drm_wait_one_vblank(struct drm_device *dev, > unsigned int pipe) > { > struct drm_vblank_crtc *vblank = drm_vblank_crtc(dev, pipe); > int ret; > - u64 last; > + u64 last, curr; > > if (drm_WARN_ON(dev, pipe >= dev->num_crtcs)) > return; > @@ -1305,7 +1305,12 @@ void drm_wait_one_vblank(struct drm_device *dev, > unsigned int pipe) > last != drm_vblank_count(dev, pipe), > msecs_to_jiffies(100)); > > - drm_WARN(dev, ret == 0, "vblank wait timed out on crtc %i\n", pipe); > + curr = drm_vblank_count(dev, pipe); > + > + if (ret == 0) { > + drm_dbg_kms(dev, "WAIT_VBLANK: timeout crtc=%d, last=%llu, > curr=%llu\n", > + pipe, last, curr); It should at the very least be a drm_err(). Though the backtrace can be useful in figuring out where the problem is coming from, so not too happy about this change. > + } > > drm_vblank_put(dev, pipe); > } > -- > 2.43.0 -- Ville Syrjälä Intel
