linux-kernel - Re: [PATCH v4 0/3] task_work_add (was: task_work

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Date:	Sat, 14 Apr 2012 05:28:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	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 v4 0/3] task_work_add (was: task_work_queue)

On 04/13, Linus Torvalds wrote:
>
> On Fri, Apr 13, 2012 at 7:12 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Changes based on review from Andrew:
> >
> >        - s/task_work_queue/task_work_add/
> >
> >        - don't create a secret dependency upon task_work.h
> >          including sched.h in tracehook.h and keys/internal.h
> >
> >        - add more includes into task_work.[ch] to not rely
> >          on "sched.h includes everything"
>
> I thought based on Andrew's comments that you were going to remove the
> extra code to do FIFO for no obvious reason.

No, I tried to defense fifo,

> Apparently nothing
> actually wanted/needed it,

True, currently nothing. And most probably never will. task_work_add()
should only be used for the "unlikely" events.

> so why do it?

I can remove it.

But, unless you strongly object, personally I'd prefer to keep fifo.

Once again. Imho of course, but fifo is simply "obviously better"
from the common sense pov when it comes to submit-the-work-for-
execution.

For example. keyctl_session_to_parent() does _cancel only to protect
from exploits doing keyctl(KEYCTL_SESSION_TO_PARENT) in an endless
loop. It could simply do task_work_add(), but in this case we need
fifo for correctness.

But, again, again, I am not going to argue too much.

Oleg.

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