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Date: Wed, 20 Jul 2011 01:04:21 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>, Andrew Morton <akpm@linux-foundation.org>,
        Nick Piggin <npiggin@kernel.dk>, linux-kernel@vger.kernel.org,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] vfs: fix race in rcu lookup of pruned dentry
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On Tue, Jul 19, 2011 at 04:56:51PM -0700, Linus Torvalds wrote:
> On Tue, Jul 19, 2011 at 4:45 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > You know what... ?I doubt that you want to mess with ->d_seq checks here.
> 
> I'm ok with doing just the "move *inode setting" patch.
> 
> And if we really don't even allow renames of those mounted things, I
> guess the sequence number isn't required.

See vfs_rename_{dir,other}:

        error = -EBUSY;
        if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
                goto out;

in both, before even trying to call the method.  Traditional on all
Unices I've ever seen...