linux-kernel - Re: [2.6.26-rc4] mount.nfsv4/memory poisoning issues...

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Message-Id: <1213127909.20459.48.camel@localhost>
Date:	Tue, 10 Jun 2008 15:58:29 -0400
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	Daniel J Blueman <daniel.blueman@...il.com>,
	linux-nfs@...r.kernel.org, nfsv4@...ux-nfs.org,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [2.6.26-rc4] mount.nfsv4/memory poisoning issues...

On Tue, 2008-06-10 at 15:13 -0400, Jeff Layton wrote:

> I think you're basically correct, but it looks to me like the
> nfs_callback_mutex actually protects nfs_callback_info.task as well.
> 
> If we're starting the thread, then we can't call kthread_stop on it
> until we release the mutex. So the thread can't exit until we release
> the mutex, and we can be guaranteed that this:
> 
>      nfs_callback_info.task = NULL;
> 
> ...can't happen until after kthread_run returns and nfs_callback_up
> sets it.
> 
> If that's right, then maybe this (untested, RFC only) patch would make sense?

Hmm... I suppose that is correct, but what if nfs_alloc_client() does

	nfs_callback_up();
	<kstrdup() fails>
	nfs_callback_down();

AFAICS, if nfs_callback_down() gets called before the kthread() function
gets scheduled back in, then you can get left with a value of
nfs_callback_info.task != NULL, since nfs_callback_svc() will never be
called.

Wouldn't it therefore make more sense to clear nfs_callback_info.task in
nfs_callback_down()?

Cheers
  Trond

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