Hi
Am 01.10.25 um 05:32 schrieb Chintan Patel:
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]>
---
drivers/gpu/drm/drm_vblank.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 46f59883183d..c8dd9d4be26c 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 +1305,20 @@ 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) {
if (!ret)
+ /*
+ * Avoid spamming WARNs for timeouts which can be caused by
+ * heavy scheduling pressure or invalid userspace calls
(fuzzing).
+ * Use debug message instead.
+ */
The comment is not necessary. The commit description gives a good rational.
+ drm_dbg_kms(dev, "WAIT_VBLANK: timeout crtc=%d, last=%llu,
curr=%llu\n",
+ pipe, last, curr);
+ } else {
+ drm_dbg_kms(dev, "WAIT_VBLANK: completed crtc=%d, last=%llu,
curr=%llu\n",
+ pipe, last, curr);
+ }
Rather drop the else branch.
Best regards
Thomas
drm_vblank_put(dev, pipe);
}
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
