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

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Date:	Tue, 27 Jan 2015 08:48:28 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Torvald Riegel <triegel@...hat.com>,
	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>,
	Arnd Bergmann <arnd@...db.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux API <linux-api@...r.kernel.org>,
	Darren Hart <dvhart@...radead.org>,
	Anton Blanchard <anton@...ba.org>,
	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

Hello Torvald,

On 01/24/2015 02:12 PM, Torvald Riegel wrote:
> On Sat, 2015-01-24 at 12:35 +0100, Thomas Gleixner wrote:
>> So we should never see -EINTR in the case of a spurious wakeup here.
>>
>> But, here is the not so good news:
>>
>>  I did some archaeology. The restart handling of futex_wait() got
>>  introduced in kernel 2.6.22, so anything older than that will have
>>  the spurious -EINTR issues.
>>
>> futex_wait_pi() always had the restart handling and glibc folks back
>> then (2006) requested that it should never return -EINTR, so it
>> unconditionally restarts the syscall whether a signal had been
>> delivered or not.
>>
>> So kernels >= 2.6.22 should never return -EINTR spuriously. If that
>> happens it's a bug and needs to be fixed.
> 
> Thanks for looking into this.
> 
> Michael, can you include the above in the documentation please?  This is
> useful for userspace code like glibc that expects a minimum kernel
> version.  Thanks!

I've added some text to my draft to cover this point.

Cheers,

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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