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Date: Mon, 25 Jun 2012 07:03:57 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        ". James Morris" <jmorris@namei.org>,
        linux-security-module@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: deferring __fput()
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On Sun, Jun 24, 2012 at 05:33:10PM +0200, Oleg Nesterov wrote:
> No, we can't do this?
> 
> OK, perhaps we can check something else instead of PF_EXITING.
> But somehow we should ensuree that if task_work_add(twork) succeeds,
> then twork->func() will be called. IOW, if task_work_add() races with
> the exiting task, it should not succeed after exit_task_work().

Hrm...  I still think that callers can bloody well check it themselves,
but anyway - we can add a new PF_... bit and have it set on kernel threads
(all along) and during exit_task_work(); the real question is in locking
and barriers needed there.  Suggestions?