linux-kernel - Re: [GIT PULL] 9p file system bug fixes for 2.6.35-rc2

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Date:	Mon, 7 Jun 2010 17:48:54 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...IV.linux.org.uk>
cc:	Eric Van Hensbergen <ericvh@...il.com>,
	V9FS Developers <v9fs-developer@...ts.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] 9p file system bug fixes for 2.6.35-rc2

On Tue, 8 Jun 2010, Al Viro wrote:

> On Mon, Jun 07, 2010 at 05:08:19PM -0700, Linus Torvalds wrote:
> 
> > In fact, the other thing that I find doing that whole "dentry->d_parent" 
> > thing seems to literally be broken. If you look at v9fs_fid_lookup(), 
> > you'll notice how it walks up the d_parent chain, and at that point you do 
> > NOT own the directory i_mutex, so at that point d_parent really _can_ be 
> > changing wildly due to concurrent renames or whatever.
> 
> Eh...  It's bogus, all right, but i_mutex is not the correct solution.

Oh, no, I didn't imply it was. But the other sites that I saw doing 
the dentry->d_parent access already _had_ the i_mutex thing, so I was 
pointing out how this one does not (and indeed _cannot_ do that).

So I'm just saying that pretty much _all_ the dentry->d_parent use in 9p 
seems very suspect. The cases where we hold i_mutex (because the caller 
already took it) shouldn't do that whole d_parent dance, because they get 
the directory inode passed into them directly.

And the other places are just buggy.

So from a quick look, the use of d_parent in 9p is simply not a good idea. 

			Linus
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