From: Trond Myklebust <trond.myklebust@fys.uio.no>
Subject: Re: [2.6.26-rc4] mount.nfsv4/memory poisoning issues...
Date: Tue, 10 Jun 2008 16:33:32 -0400
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Cc: nfsv4@linux-nfs.org, linux-nfs@vger.kernel.org,
	Daniel J Blueman <daniel.blueman@gmail.com>,
	Linux Kernel <linux-kernel@vger.kernel.org>
To: Jeff Layton <jlayton@redhat.com>
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On Tue, 2008-06-10 at 16:13 -0400, Jeff Layton wrote:

> We can't call nfs_callback_down() until after nfs_callback_up()
> returns, so we're guaranteed to have "task" set to a valid task
> (presuming that nfs_callback_up() doesn't return error). We also can't
> return from nfs_callback_down() until after the nfs_callback_svc() has
> exited. kthread_stop() will block until it does.

The code I'm alluding to is in kthread():

       /* OK, tell user we're spawned, wait for stop or wakeup */
        __set_current_state(TASK_UNINTERRUPTIBLE);
        complete(&create->started);
        schedule();

        if (!kthread_should_stop())
                ret = threadfn(data);

schedule() is called _after_ the complete() call, and _before_ we
execute threadfn() a.k.a. nfs_callback_svc(). If nfs_alloc_client() has
time to call nfs_callback_down() before the above thread gets scheduled
back in, then threadfn() doesn't get called at all, since
kthread_should_stop() is true.

Cheers
  Trond