linux-kernel - Re: Linux 2.6.26-rc4

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Message-Id: <1212514104.3025.110.camel@raven.themaw.net>
Date:	Wed, 04 Jun 2008 01:28:23 +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 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.

> inode is freed
> vfs_readdir() releases i_mutex - in already freed struct inode.

But it could happen later. So it's academic I guess.

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

Yeah, I'll look into why I believed I needed to turn the dentry
negative. I'll need to keep the dentry positive through out this
process.

Ian


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