On 10/1/25 23:34, Thomas Zimmermann wrote:
Hi
Am 02.10.25 um 04:57 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]>
There should be no empty lines among those tags
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);
Please don't call drm_vblank_count() here. It's not necessary for
regular operation. Simply keep the debug message as-is.
+
+ if (ret == 0) {
"if (!ret)" is the preferred style.
+ drm_dbg_kms(dev, "WAIT_VBLANK: timeout crtc=%d, last=%llu,
curr=%llu\n",
+ pipe, last, curr);
Aligning the pipe argument with dev from the previous line is the
preferred style.
Hi Thomas,
Thank you for your review and helpful suggestions.
I’ll drop the unnecessary comment and remove the else branch as you
recommended.
I’ll send a v3 with these changes.
Best regards,
Chintan
