Re: futex(2) man page update help request - Michael Kerrisk (man-pages)

From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: mtk.manpages@gmail.com, "Carlos O'Donell" <carlos@redhat.com>,
	Darren Hart <dvhart@linux.intel.com>, Ingo Molnar <mingo@elte.hu>,
	Jakub Jelinek <jakub@redhat.com>,
	"linux-man@vger.kernel.org" <linux-man@vger.kernel.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Davidlohr Bueso <davidlohr.bueso@hp.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Linux API <linux-api@vger.kernel.org>,
	Torvald Riegel <triegel@redhat.com>,
	Roland McGrath <roland@redhat.com>,
	Darren Hart <dvhart@infradead.org>,
	Anton Blanchard <anton@samba.org>, Petr Baudis <pasky@suse.cz>,
	Eric Dumazet <edumazet@google.com>,
	bill o gallmeister <bgallmeister@gmail.com>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	Daniel Wagner <wagi@monom.org>, Rich Felker <dalias@libc.org>
Subject: Re: futex(2) man page update help request
Date: Fri, 16 Jan 2015 21:54:10 +0100	[thread overview]
Message-ID: <54B97A72.2050205@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1501161618080.5526@nanos>

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/