linux-kernel - Re: futex(2) man page update help request

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Date:	Fri, 16 Jan 2015 21:54:10 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	mtk.manpages@...il.com, Carlos O'Donell <carlos@...hat.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux API <linux-api@...r.kernel.org>,
	Torvald Riegel <triegel@...hat.com>,
	Roland McGrath <roland@...hat.com>,
	Darren Hart <dvhart@...radead.org>,
	Anton Blanchard <anton@...ba.org>, Petr Baudis <pasky@...e.cz>,
	Eric Dumazet <edumazet@...gle.com>,
	bill o gallmeister <bgallmeister@...il.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Daniel Wagner <wagi@...om.org>, Rich Felker <dalias@...c.org>
Subject: Re: futex(2) man page update help request

On 01/16/2015 04:20 PM, Thomas Gleixner wrote:
> On Fri, 16 Jan 2015, Michael Kerrisk (man-pages) wrote:
> 
>> Hello Thomas,
>>
>> On 01/15/2015 11:23 PM, Thomas Gleixner wrote:
>>> On Thu, 15 Jan 2015, Michael Kerrisk (man-pages) wrote:
>>>>> [EINVAL] uaddr equal uaddr2. Requeue to same futex.
>>>>
>>>> ??? I added this, but does this error not occur only for PI requeues?
>>>
>>> It's equally wrong for normal futexes. And its actually the same code
>>> checking for this for all variants.
>>
>> I don't understand "equally wrong" in your reply, I'm sorry. Do you
>> mean:
>>
>> a) This error text should be there for both normal and PI requeues
> 
> It is there for both. The requeue code has that check independent of
> the requeue type (normal/pi). It never makes sense to requeue
> something to itself whether normal or pi futex. We added this for PI,
> because there it is harmful, but we did not special case it. So normal
> futexes get the same treatment.

Hello Thomas, 

Color me stupid, but I can't see this in futex_requeue(). Where is that
check that is "independent of the requeue type (normal/pi)"?

When I look through futex_requeue(), all the likely looking sources
of EINVAL are governed by a check on the 'requeue_pi' argument.

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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