Re: [PATCH] videobuf2-core: take mmap_sem before calling __qbuf_userptr

[Jan Kara]

On Fri 22-08-14 18:01:09, Hans Verkuil wrote:
> Commit f035eb4e976ef5a059e30bc91cfd310ff030a7d3 (videobuf2: fix lockdep 
> warning)
> unfortunately removed the mmap_sem lock that is needed around the call to
> __qbuf_userptr. Amazingly nobody noticed this until Jan Kara pointed this out
> to me.
> 
> Signed-off-by: Hans Verkuil <hans.verk...@cisco.com>
> Reported-by: Jan Kara <j...@suse.cz>
...
> @@ -1627,7 +1628,9 @@ static int __buf_prepare(struct vb2_buffer *vb, const 
> struct v4l2_buffer *b)
>               ret = __qbuf_mmap(vb, b);
>               break;
>       case V4L2_MEMORY_USERPTR:
  I guess you are missing something like:

mmap_sem = &current->mm->mmap_sem;

                                                                Honza
> +             down_read(mmap_sem);
>               ret = __qbuf_userptr(vb, b);
> +             up_read(mmap_sem);
>               break;
>       case V4L2_MEMORY_DMABUF:
>               ret = __qbuf_dmabuf(vb, b);
> -- 
> 2.0.1
> 
-- 
Jan Kara <j...@suse.cz>
SUSE Labs, CR
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