[PATCH] drm/fbdev-shmem: don't warn on a transient dirty callback failure

[PATCH] drm/fbdev-shmem: don't warn on a transient dirty callback failure

[xujiahao]

The fbdev dirty callback (drm_atomic_helper_dirtyfb()) can fail with
-ENOMEM when the atomic commit allocation fails under memory pressure.
That is a transient runtime condition, not a driver bug: the damage is
only cosmetic and the frame is redrawn on the next flush.

drm_WARN_ONCE() turns this recoverable failure into a WARN splat (and a
panic with panic_on_warn), which syzbot keeps reporting:

  virtio-pci 0000:00:01.0: [drm] Dirty helper failed: ret=-12
  WARNING: drivers/gpu/drm/drm_fbdev_shmem.c:118 at ...

Keep the warning for other failures, but do not warn about -ENOMEM.  The
error is still propagated to the caller.

Reported-by: syzbot+369ee6a6e9d0bbf14b37@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=369ee6a6e9d0bbf14b37
Signed-off-by: xujiahao <xujiahao@cmss.chinamobile.com>
---
 drivers/gpu/drm/drm_fbdev_shmem.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fbdev_shmem.c b/drivers/gpu/drm/drm_fbdev_shmem.c
index 8eb05fe9b..c3fa5a663 100644
--- a/drivers/gpu/drm/drm_fbdev_shmem.c
+++ b/drivers/gpu/drm/drm_fbdev_shmem.c
@@ -115,7 +115,14 @@ static int drm_fbdev_shmem_helper_fb_dirty(struct drm_fb_helper *helper,
 
 	if (helper->fb->funcs->dirty) {
 		ret = helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, clip, 1);
-		if (drm_WARN_ONCE(dev, ret, "Dirty helper failed: ret=%d\n", ret))
+		/*
+		 * An allocation failure is a transient condition under memory
+		 * pressure, not a driver bug, so don't warn about it.  The
+		 * error itself is still propagated to the caller.
+		 */
+		drm_WARN_ONCE(dev, ret && ret != -ENOMEM,
+			      "Dirty helper failed: ret=%d\n", ret);
+		if (ret)
 			return ret;
 	}
 
-- 
2.43.0

Re: [PATCH] drm/fbdev-shmem: don't warn on a transient dirty callback failure

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential
issues to consider:
- [High] drm/fbdev-shmem: single-word handle used in Author and
  Signed-off-by
- [Low] drm/fbdev-shmem: missing Fixes trailer for
  drm_fbdev_shmem_helper_fb_dirty()
--

commit 3bcd442074e2ca85eb8c3537eb31d873b7b1b756
Author: xujiahao <xujiahao@cmss.chinamobile.com>

> drm/fbdev-shmem: don't warn on a transient dirty callback failure
>
> The fbdev dirty callback (drm_atomic_helper_dirtyfb()) can fail with
> -ENOMEM when the atomic commit allocation fails under memory pressure.
> That is a transient runtime condition, not a driver bug: the damage is
> only cosmetic and the frame is redrawn on the next flush.
>
> drm_WARN_ONCE() turns this recoverable failure into a WARN splat (and a
> panic with panic_on_warn), which syzbot keeps reporting:
>
>   virtio-pci 0000:00:01.0: [drm] Dirty helper failed: ret=-12
>   WARNING: drivers/gpu/drm/drm_fbdev_shmem.c:118 at ...
>
> Keep the warning for other failures, but do not warn about -ENOMEM.  The
> error is still propagated to the caller.
>
> Reported-by: syzbot+369ee6a6e9d0bbf14b37@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=369ee6a6e9d0bbf14b37
> Signed-off-by: xujiahao <xujiahao@cmss.chinamobile.com>

[Severity: High]
Both the Author field and the Signed-off-by trailer use the single-word
handle "xujiahao" instead of a full real name.  Per
Documentation/process/submitting-patches.rst, the Developer's Certificate of
Origin requires signing off with a full human name (for example, "Jiahao
Xu").

[Severity: Low]
This fixes a false-positive warning in drm_fbdev_shmem_helper_fb_dirty().
Should the commit message include a Fixes: trailer?

  Fixes: 150f431a0831 ("drm/fbdev: Add fbdev-shmem")
  Fixes: f0f195d1a3ae ("drm/fbdev-shmem: Support struct drm_driver.fbdev_probe")

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261111114108.675721-1-xujiahao@cmss.chinamobile.com?part=1