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.
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: [email protected] Closes: https://syzkaller.appspot.com/bug?extid=147ba789658184f0ce04 Tested-by: [email protected] Signed-off-by: Chintan Patel <[email protected]> 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); + } drm_vblank_put(dev, pipe); } -- 2.43.0
