* [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery
@ 2026-04-20 11:35 Matan Cohen
2026-04-20 12:35 ` Greg KH
2026-04-20 14:14 ` Dan Carpenter
0 siblings, 2 replies; 5+ messages in thread
From: Matan Cohen @ 2026-04-20 11:35 UTC (permalink / raw)
To: linux-staging; +Cc: parthiban.veerasooran, christian.gromm, gregkh, Matan Cohen
BUG_ON() halts the kernel unconditionally. The check after
most_deregister_component() guards against a bug in mostcore: it
currently does not call disconnect_channel() for linked channels on
deregistration, so if that ever changes unexpectedly, video_devices
could be non-empty.
Replace BUG_ON with WARN_ON_ONCE so the kernel stays up, and add a
recovery path that drains and frees any remaining devices to avoid
memory leaks in that error case.
Also document what the spinlock and mutex in struct most_video_dev
each protect.
---
drivers/staging/most/video/video.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
index 04351f8ccccf1..4ade49569bd63 100644
--- a/drivers/staging/most/video/video.c
+++ b/drivers/staging/most/video/video.c
@@ -33,14 +33,14 @@ struct most_video_dev {
bool mute;
struct list_head pending_mbos;
- spinlock_t list_lock;
+ spinlock_t list_lock; /* protects pending_mbos and mute */
struct v4l2_device v4l2_dev;
atomic_t access_ref;
struct video_device *vdev;
unsigned int ctrl_input;
- struct mutex lock;
+ struct mutex lock; /* v4l2 device lock */
wait_queue_head_t wait_data;
};
@@ -577,7 +577,20 @@ static void __exit comp_exit(void)
most_deregister_configfs_subsys(&comp);
most_deregister_component(&comp);
- BUG_ON(!list_empty(&video_devices));
+
+ if (WARN_ON_ONCE(!list_empty(&video_devices))) {
+ /* clean up any devices unexpectedly added during deregister phase */
+ spin_lock_irq(&list_lock);
+ list_replace_init(&video_devices, &free_list);
+ spin_unlock_irq(&list_lock);
+
+ list_for_each_entry_safe(mdev, tmp, &free_list, list) {
+ list_del_init(&mdev->list);
+ comp_unregister_videodev(mdev);
+ v4l2_device_disconnect(&mdev->v4l2_dev);
+ v4l2_device_put(&mdev->v4l2_dev);
+ }
+ }
}
module_init(comp_init);
--
2.43.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery
2026-04-20 11:35 [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery Matan Cohen
@ 2026-04-20 12:35 ` Greg KH
2026-04-20 14:14 ` Dan Carpenter
1 sibling, 0 replies; 5+ messages in thread
From: Greg KH @ 2026-04-20 12:35 UTC (permalink / raw)
To: Matan Cohen; +Cc: linux-staging, parthiban.veerasooran, christian.gromm
On Mon, Apr 20, 2026 at 11:35:03AM +0000, Matan Cohen wrote:
> BUG_ON() halts the kernel unconditionally. The check after
> most_deregister_component() guards against a bug in mostcore: it
> currently does not call disconnect_channel() for linked channels on
> deregistration, so if that ever changes unexpectedly, video_devices
> could be non-empty.
>
> Replace BUG_ON with WARN_ON_ONCE so the kernel stays up, and add a
> recovery path that drains and frees any remaining devices to avoid
> memory leaks in that error case.
>
> Also document what the spinlock and mutex in struct most_video_dev
> each protect.
> ---
> drivers/staging/most/video/video.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
> index 04351f8ccccf1..4ade49569bd63 100644
> --- a/drivers/staging/most/video/video.c
> +++ b/drivers/staging/most/video/video.c
> @@ -33,14 +33,14 @@ struct most_video_dev {
> bool mute;
>
> struct list_head pending_mbos;
> - spinlock_t list_lock;
> + spinlock_t list_lock; /* protects pending_mbos and mute */
>
> struct v4l2_device v4l2_dev;
> atomic_t access_ref;
> struct video_device *vdev;
> unsigned int ctrl_input;
>
> - struct mutex lock;
> + struct mutex lock; /* v4l2 device lock */
>
> wait_queue_head_t wait_data;
> };
> @@ -577,7 +577,20 @@ static void __exit comp_exit(void)
>
> most_deregister_configfs_subsys(&comp);
> most_deregister_component(&comp);
> - BUG_ON(!list_empty(&video_devices));
> +
> + if (WARN_ON_ONCE(!list_empty(&video_devices))) {
> + /* clean up any devices unexpectedly added during deregister phase */
> + spin_lock_irq(&list_lock);
> + list_replace_init(&video_devices, &free_list);
> + spin_unlock_irq(&list_lock);
> +
> + list_for_each_entry_safe(mdev, tmp, &free_list, list) {
> + list_del_init(&mdev->list);
> + comp_unregister_videodev(mdev);
> + v4l2_device_disconnect(&mdev->v4l2_dev);
> + v4l2_device_put(&mdev->v4l2_dev);
> + }
> + }
> }
>
> module_init(comp_init);
> --
> 2.43.0
>
>
Hi,
This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him
a patch that has triggered this response. He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created. Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.
You are receiving this message because of the following common error(s)
as indicated below:
- Your patch does not have a Signed-off-by: line. Please read the
kernel file, Documentation/process/submitting-patches.rst and resend
it after adding that line. Note, the line needs to be in the body of
the email, before the patch, not at the bottom of the patch or in the
email signature.
- Your patch did many different things all at once, making it difficult
to review. All Linux kernel patches need to only do one thing at a
time. If you need to do multiple things (such as clean up all coding
style issues in a file/driver), do it in a sequence of patches, each
one doing only one thing. This will make it easier to review the
patches to ensure that they are correct, and to help alleviate any
merge issues that larger patches can cause.
If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.
thanks,
greg k-h's patch email bot
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery
2026-04-20 11:35 [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery Matan Cohen
2026-04-20 12:35 ` Greg KH
@ 2026-04-20 14:14 ` Dan Carpenter
2026-04-21 15:15 ` Matan Cohen
1 sibling, 1 reply; 5+ messages in thread
From: Dan Carpenter @ 2026-04-20 14:14 UTC (permalink / raw)
To: Matan Cohen; +Cc: linux-staging, parthiban.veerasooran, christian.gromm, gregkh
On Mon, Apr 20, 2026 at 11:35:03AM +0000, Matan Cohen wrote:
> BUG_ON() halts the kernel unconditionally. The check after
> most_deregister_component() guards against a bug in mostcore: it
> currently does not call disconnect_channel() for linked channels on
> deregistration, so if that ever changes unexpectedly, video_devices
> could be non-empty.
>
> Replace BUG_ON with WARN_ON_ONCE so the kernel stays up, and add a
> recovery path that drains and frees any remaining devices to avoid
> memory leaks in that error case.
>
> Also document what the spinlock and mutex in struct most_video_dev
> each protect.
> ---
> drivers/staging/most/video/video.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
> index 04351f8ccccf1..4ade49569bd63 100644
> --- a/drivers/staging/most/video/video.c
> +++ b/drivers/staging/most/video/video.c
> @@ -33,14 +33,14 @@ struct most_video_dev {
> bool mute;
>
> struct list_head pending_mbos;
> - spinlock_t list_lock;
> + spinlock_t list_lock; /* protects pending_mbos and mute */
I always dread these kinds of patches... The comment is useless. Way
too vague and kind of wrong also. I want to see a much more thorough
explanation.
regards,
dan carpenter
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery
2026-04-20 14:14 ` Dan Carpenter
@ 2026-04-21 15:15 ` Matan Cohen
2026-04-21 15:22 ` Greg KH
0 siblings, 1 reply; 5+ messages in thread
From: Matan Cohen @ 2026-04-21 15:15 UTC (permalink / raw)
To: Dan Carpenter
Cc: linux-staging, parthiban.veerasooran, christian.gromm, gregkh
On Mon, Apr 20, 2026, at 5:14 PM, Dan Carpenter wrote:
> I always dread these kinds of patches... The comment is useless. Way
> too vague and kind of wrong also. I want to see a much more thorough
> explanation.
Hi Dan and Greg's bot,
First of All Thank you for the review and quick reply.
This is my first time Contributing, I wanted to start with something well contained that I found using checkpatch.pl
My intention was twofold:
1. Replace BUG_ON with WARN_ON_ONCE — the kernel should not crash
unconditionally here since the cleanup above already completed.
2. Add a recovery path to drain any remaining devices and avoid a
memory leak, in case something unexpectedly adds to video_devices, during the deregistration calls.
- I think that this was the original intention that lead the BUG_ON to be there in the first place, but I am not entirely sure.
I'll resend as v2 with:
- The lock comments into a separate Patch
- A Signed-off-by line (apologies for missing that, my bad)
- A more thorough commit message
Should I keep the recovery path with a better explanation, or drop it
and use a bare WARN_ON_ONCE?
waiting for your reply before spamming with random update, let me know what you think?
Regards,
Matan Cohen
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery
2026-04-21 15:15 ` Matan Cohen
@ 2026-04-21 15:22 ` Greg KH
0 siblings, 0 replies; 5+ messages in thread
From: Greg KH @ 2026-04-21 15:22 UTC (permalink / raw)
To: Matan Cohen
Cc: Dan Carpenter, linux-staging, parthiban.veerasooran,
christian.gromm
On Tue, Apr 21, 2026 at 06:15:29PM +0300, Matan Cohen wrote:
> On Mon, Apr 20, 2026, at 5:14 PM, Dan Carpenter wrote:
> > I always dread these kinds of patches... The comment is useless. Way
> > too vague and kind of wrong also. I want to see a much more thorough
> > explanation.
>
> Hi Dan and Greg's bot,
>
> First of All Thank you for the review and quick reply.
> This is my first time Contributing, I wanted to start with something well contained that I found using checkpatch.pl
>
> My intention was twofold:
>
> 1. Replace BUG_ON with WARN_ON_ONCE — the kernel should not crash
> unconditionally here since the cleanup above already completed.
Note, you have trailing whitespace in yoru email client, please fix that
up.
Anyway, you can not replace BUG_ON() with WARN_ON() and expect the crash
to go away due to panic-on-warn being an option that a few billion Linux
systems have. If this type of thing can happen, then handle it properly
and deal with it, otherwise if it is so bad that all data will be lost,
live with the BUG_ON().
thanks,
greg k-h
^ permalink raw reply [flat|nested] 5+ messages in thread
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2026-04-20 11:35 [PATCH] staging: most: video: replace BUG_ON with WARN_ON_ONCE and add recovery Matan Cohen
2026-04-20 12:35 ` Greg KH
2026-04-20 14:14 ` Dan Carpenter
2026-04-21 15:15 ` Matan Cohen
2026-04-21 15:22 ` Greg KH
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