linux-kernel - Re: Linux 2.6.26-rc4

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Message-ID: <20080603165042.GC28946@ZenIV.linux.org.uk>
Date:	Tue, 3 Jun 2008 17:50:42 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ian Kent <raven@...maw.net>, 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, 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()
inode is freed
vfs_readdir() releases i_mutex - in already freed struct inode.

Hell, just getdents() right *after* dentry->d_inode = NULL will oops,
plain and simple.
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