linux-kernel - Re: Linux 2.6.26-rc4

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Message-Id: <1212514893.3025.123.camel@raven.themaw.net>
Date:	Wed, 04 Jun 2008 01:41:32 +0800
From:	Ian Kent <raven@...maw.net>
To:	Al Viro <viro@...IV.linux.org.uk>
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 Tue, 2008-06-03 at 18:41 +0100, Al Viro wrote:
> 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).

OK, I'll need to look at vfs_readdir().
I thought vfs_readdir() would take the containing directory mutex as
does ->lookup().


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