From mboxrd@z Thu Jan  1 00:00:00 1970
From: Al Viro <viro@ZenIV.linux.org.uk>
Subject: Re: [PATCH 1/5] Safer nfsd_cross_mnt()
Date: Wed, 22 Apr 2009 20:17:19 +0100
Message-ID: <20090422191719.GN8633@ZenIV.linux.org.uk>
References: <E1LwNkj-0004WN-AZ@ZenIV.linux.org.uk> <20090422180641.GB9541@fieldses.org>
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Cc: Al Viro <viro-rfM+Q5joDG/XmaaqVzeoHQ@public.gmane.org>, linux-nfs@vger.kernel.org
To: "J. Bruce Fields" <bfields@fieldses.org>
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On Wed, Apr 22, 2009 at 02:06:41PM -0400, J. Bruce Fields wrote:
> On Tue, Apr 21, 2009 at 09:43:41PM +0000, Al Viro wrote:
> > 
> > AFAICS, we have a subtle bug there: if we have crossed mountpoint
> > *and* it got mount --move'd away, we'll be holding only one
> > reference to fs containing dentry - exp->ex_path.mnt.  IOW, we
> > ought to dput() before exp_put().
> 
> OK.  So a dentry of its own doesn't hold any reference on its
> filesystem?

Nope.  That's why you want vfsmount or superblock reference.
And export *does* contain vfsmount reference, so everything's fine,
provided that you drop them in the right order.