Re: [PATCH] vfs: automount should ignore LOOKUP_FOLLOW

Re: [PATCH] vfs: automount should ignore LOOKUP_FOLLOW

[Jeff Layton]

On Mon, 05 Sep 2011 18:06:26 +0200
Miklos Szeredi <miklos@szeredi.hu> wrote:

> From: Miklos Szeredi <mszeredi@suse.cz>
> 
> Prior to 2.6.38 automount would not trigger on either stat(2) or
> lstat(2) on the automount point.
> 
> After 2.6.38, with the introduction of the ->d_automount()
> infrastructure, stat(2) and others would start triggering automount
> while lstat(2), etc. still would not.  This is a regression and a
> userspace ABI change.
> 
> Problem originally reported here:
> 
>   http://thread.gmane.org/gmane.linux.kernel.autofs/6098
> 
> It appears that there was an attempt at fixing various userspace tools
> to not trigger the automount.  But since the stat system call is
> rather common it is impossible to "fix" all userspace.
> 
> This patch reverts the original behavior, which is to not trigger on
> stat(2) and other symlink following syscalls.
> 
> Reported-by: Leonardo Chiquitto <leonardo.lists@gmail.com>
> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
> CC: David Howells <dhowells@redhat.com>
> CC: Ian Kent <raven@themaw.net>
> CC: stable@kernel.org
> ---
>  fs/namei.c |   33 +++++++++++++++------------------
>  1 file changed, 15 insertions(+), 18 deletions(-)
> 

This patch is causing a regression with NFSv4.

When I mount up a filesystem, and do any activity on it, a new
automount gets triggered on top of the original mountpoint.

The first mount ends up getting the fsid of the pseudo root (fsid=0),
rather than the correct one for the fs. Once it traverses into the
actual filesystem the fsid's look different and d_automount gets
triggered.

I think the problem is that nfs_follow_remote_path() uses
LOOKUP_FOLLOW, and with the above patch this is now ignored.

Let me know if you need details on how to reproduce this.

-- 
Jeff Layton <jlayton@redhat.com>