media: vb2: frame_vector.c: replace WARN_ONCE with a comment
Commit Message
The WARN_ONCE was issued also in cases that had nothing to do with VM_IO
(e.g. if the start address was just a random value and uaccess fails with
-EFAULT).
There are no reports of WARN_ONCE being issued for actual VM_IO cases, so
just drop it and instead add a note to the comment before the function.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
Comments
On 17/08/2023 12:41, Hans Verkuil wrote:
> The WARN_ONCE was issued also in cases that had nothing to do with VM_IO
> (e.g. if the start address was just a random value and uaccess fails with
> -EFAULT).
>
> There are no reports of WARN_ONCE being issued for actual VM_IO cases, so
> just drop it and instead add a note to the comment before the function.
>
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
I forgot to add:
Reported-by: Yikebaer Aizezi <yikebaer61@gmail.com>
> ---
> diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c
> index 0f430ddc1f67..fd87747be9b1 100644
> --- a/drivers/media/common/videobuf2/frame_vector.c
> +++ b/drivers/media/common/videobuf2/frame_vector.c
> @@ -31,6 +31,10 @@
> * different type underlying the specified range of virtual addresses.
> * When the function isn't able to map a single page, it returns error.
> *
> + * Note that get_vaddr_frames() cannot follow VM_IO mappings. It used
> + * to be able to do that, but that could (racily) return non-refcounted
> + * pfns.
> + *
> * This function takes care of grabbing mmap_lock as necessary.
> */
> int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
> @@ -59,8 +63,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
> if (likely(ret > 0))
> return ret;
>
> - /* This used to (racily) return non-refcounted pfns. Let people know */
> - WARN_ONCE(1, "get_vaddr_frames() cannot follow VM_IO mapping");
> vec->nr_frames = 0;
> return ret ? ret : -EFAULT;
> }
>
@@ -31,6 +31,10 @@
* different type underlying the specified range of virtual addresses.
* When the function isn't able to map a single page, it returns error.
*
+ * Note that get_vaddr_frames() cannot follow VM_IO mappings. It used
+ * to be able to do that, but that could (racily) return non-refcounted
+ * pfns.
+ *
* This function takes care of grabbing mmap_lock as necessary.
*/
int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
@@ -59,8 +63,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, bool write,
if (likely(ret > 0))
return ret;
- /* This used to (racily) return non-refcounted pfns. Let people know */
- WARN_ONCE(1, "get_vaddr_frames() cannot follow VM_IO mapping");
vec->nr_frames = 0;
return ret ? ret : -EFAULT;
}