[PATCH v2] drm/fbdev-shmem: don't warn on a transient dirty callback failure

[PATCH v2] drm/fbdev-shmem: don't warn on a transient dirty callback failure

[Jiahao Xu]

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.

Fixes: 150f431a0831 ("drm/fbdev: Add fbdev-shmem")
Reported-by: syzbot+369ee6a6e9d0bbf14b37@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=369ee6a6e9d0bbf14b37
Signed-off-by: Jiahao Xu <xujiahao@cmss.chinamobile.com>
---
v2:
 - Add the Fixes: tag reported by sashiko-bot.  No code change.
---
 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 v2] drm/fbdev-shmem: don't warn on a transient dirty callback failure

[Thomas Zimmermann]

Am 11.11.26 um 05:41 schrieb Jiahao Xu:
> 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.

Cosmetic? Failing to allocate memory seems like a significant problem to me.

>
> 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.
>
> Fixes: 150f431a0831 ("drm/fbdev: Add fbdev-shmem")
> Reported-by: syzbot+369ee6a6e9d0bbf14b37@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=369ee6a6e9d0bbf14b37
> Signed-off-by: Jiahao Xu <xujiahao@cmss.chinamobile.com>
> ---
> v2:
>   - Add the Fixes: tag reported by sashiko-bot.  No code change.
> ---
>   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;
>   	}
>   

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)