Subject: Re: [PATCH] nfs: Do not allow multiple mounts on same mountpoint
 when using -o noac
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Sachin Prabhu <sprabhu@redhat.com>
Cc: NFS <linux-nfs@vger.kernel.org>
Date: Sat, 30 Jul 2011 14:33:05 -0400
In-Reply-To: <1311947408.29400.40.camel@sprabhu.fab.redhat.com>
References: <1311947408.29400.40.camel@sprabhu.fab.redhat.com>
Content-Type: text/plain; charset="UTF-8"
Message-ID: <1312050785.26265.2.camel@lade.trondhjem.org>
Sender: linux-nfs-owner@vger.kernel.org
MIME-Version: 1.0

On Fri, 2011-07-29 at 14:50 +0100, Sachin Prabhu wrote: 
> When you normally attempt to mount a share twice on the same mountpoint,
> a check in do_add_mount causes it to return an error
> 
> # mount localhost:/nfsv3 /mnt
> # mount localhost:/nfsv3 /mnt
> mount.nfs: /mnt is already mounted or busy
> 
> However when using the option 'noac', the user is able to mount the same
> share on the same mountpoint multiple times. This happens because a
> share mounted with the noac option is automatically assigned the 'sync'
> flag MS_SYNCHRONOUS in nfs_initialise_sb(). This flag is set after the
> check for already existing superblocks is done in sget(). The check for
> the mount flags in nfs_compare_mount_options() does not take into
> account the 'sync' flag applied later on in the code path. This means
> that when using 'noac', a new superblock structure is assigned for every
> new mount of the same share and multiple shares on the same mountpoint
> are allowed.
> 
> ie. 
> # mount -onoac localhost:/nfsv3 /mnt
> can be run multiple times.
> 
> The patch checks for noac and assigns the sync flag before sget() is
> called to obtain an already existing superblock structure.
> 
> 
> Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>

Hi Sachin,

This patch fails to apply with the error 'corrupt patch at line 6'. It
looks to me as if your mailer has reformatted it for you.

Cheers
  Trond
-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com