linux-kernel - Re: deferring _

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Message-ID: <20120625060357.GT14083@ZenIV.linux.org.uk>
Date:	Mon, 25 Jun 2012 07:03:57 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	". James Morris" <jmorris@...ei.org>,
	linux-security-module@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: deferring __fput()

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?
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