Re: overlayfs: regression bug from 4bacc9c9 (Make f_path always point to the overlay and f_inode to the underlay)

[Alban Crequy]

On 12 October 2015 at 15:50, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> On Wed, Oct 07, 2015 at 02:23:23PM +0200, Alban Crequy wrote:
>> Hi,
>>
>> I'm reporting an issue in overlay fs that was introduced in v4.2 (it
>> worked on v4.1): when overlay fs is mounted inside a overlay fs, I get
>> a "no such device or address" error (ENXIO) during open(). After
>> adding some debug printks, I found that the ENXIO comes from
>> fs/inode.c:no_open().
>>
>> The bug was initially reported on:
>> https://github.com/coreos/rkt/issues/1537
>>
>> The following commands can reproduce the issue:
>
> Thanks for the excellent report.
>
> See below for a fix.  Please let me know if you see any issues.

Thanks for the fix. I tested it and it fixes the test case with the
commands I wrote in my previous email.

Tested-by: Alban Crequy <alban.crequy@xxxxxxxxx>


> Thanks,
> Miklos
> ---
>
> Subject: ovl: fix open in stacked overlay
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> If two overlayfs filesystems are stacked on top of each other, then we need
> recursion in ovl_d_select_inode().
>
> I guess d_backing_inode() is supposed to do that.  But currently it doesn't
> and that functionality is open coded in vfs_open().  This is now copied
> into ovl_d_select_inode() to fix this regression.
>
> Reported-by: Alban Crequy <alban.crequy@xxxxxxxxx>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay...")
> Cc: David Howells <dhowells@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.2+
> ---
>  fs/overlayfs/inode.c |    3 +++
>  1 file changed, 3 insertions(+)
>
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -363,6 +363,9 @@ struct inode *ovl_d_select_inode(struct
>                 ovl_path_upper(dentry, &realpath);
>         }
>
> +       if (realpath.dentry->d_flags & DCACHE_OP_SELECT_INODE)
> +               return realpath.dentry->d_op->d_select_inode(realpath.dentry, file_flags);
> +
>         return d_backing_inode(realpath.dentry);
>  }
>
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