linux-kernel - Re: Linux 2.6.26-rc4

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Date:	Tue, 3 Jun 2008 18:41:25 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Ian Kent <raven@...maw.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>, jesper@...gh.cc,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Linux 2.6.26-rc4

On Wed, Jun 04, 2008 at 01:28:23AM +0800, Ian Kent wrote:
> 
> On Tue, 2008-06-03 at 17:50 +0100, Al Viro wrote:
> > On Tue, Jun 03, 2008 at 05:41:03PM +0100, Al Viro wrote:
> > 
> > > >From my reading of that code looks like it's been rmdir'ed.  And no, I
> > > don't understand what the hell is that code trying to do.
> > > 
> > > Ian, could you describe the race you are talking about?
> > 
> > BTW, this stuff is definitely broken regardless of mount - if something
> > had the directory in question opened before that rmdir and we'd hit
> > your lookup_unhashed while another CPU had been in the middle of
> > getdents(2) on that opened descriptor, we'll get
> > 
> > vfs_readdir() grabs i_mutex
> > vfs_readdir() checks that it's dead
> > autofs4_lookup_unhashed() calls iput()
> 
> Can this really happen, since autofs4_lookup_unhashed() is only called
> with the i_mutex held.

i_mutex on a different inode (obviously - it frees the inode in question,
so if caller held i_mutex on it, you would be in trouble every time you
hit that codepath).
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