linux-kernel - Re: [PATCH v5 3/3] cred: change keyctl_session_to_parent() to use task_work

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Date:	Mon, 30 Apr 2012 09:56:05 +0100
From:	David Howells <dhowells@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	dhowells@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexander Gordeev <agordeev@...hat.com>,
	Chris Zankel <chris@...kel.net>,
	David Smith <dsmith@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Larry Woodman <lwoodman@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] cred: change keyctl_session_to_parent() to use task_work_add()

Oleg Nesterov <oleg@...hat.com> wrote:

> Change keyctl_session_to_parent() to use task_work_add() and
> move key_replace_session_keyring() logic into task_work->func().
> 
> Note that we do task_work_cancel() before task_work_add() to
> ensure that only one work can be pending at any time. This is
> important, we must not allow user-space to abuse the parent's
> ->task_works list.
> 
> The callback, replace_session_keyring(), checks PF_EXITING.
> I guess this is not really needed but looks better.
> 
> As a side effect, this fixes the (unlikely) race. The callers
> of key_replace_session_keyring() and keyctl_session_to_parent()
> lack the necessary barriers, the parent can miss the request.
> 
> Now we can remove task_struct->replacement_session_keyring and
> related code.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: David Howells <dhowells@...hat.com>
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