linux-kernel - Re: [PATCH] signal: Unexport sigsuspend()

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Message-ID: <564CE3DA.8040404@nod.at>
Date:	Wed, 18 Nov 2015 21:47:22 +0100
From:	Richard Weinberger <richard@....at>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, vegard.nossum@...cle.com,
	oleg@...hat.com, amanieu@...il.com, dave@...olabs.net,
	qiaowei.ren@...el.com, luto@...capital.net, palmer@...belt.com,
	vdavydov@...allels.com
Subject: Re: [PATCH] signal: Unexport sigsuspend()

Am 18.11.2015 um 21:44 schrieb Andrew Morton:
> On Mon, 16 Nov 2015 19:18:21 +0100 Richard Weinberger <richard@....at> wrote:
> 
>> sigsuspend() is nowhere used except in signal.c itself,
>> so we can mark it static do not pollute the global namespace.
>>
>> But this patch is more than a boring cleanup patch,
>> it fixes a real issue on UserModeLinux.
>> UML has a special console driver to display ttys using xterm,
>> or other terminal emulators, on the host side.
>> Vegard reported that sometimes UML is unable to spawn a xterm
>> and he's facing the following warning:
>> WARNING: CPU: 0 PID: 908 at include/linux/thread_info.h:128 sigsuspend+0xab/0xc0()
>> It turned out that this warning makes absolutely no sense as
>> the UML xterm code calls sigsuspend() on the host side, at least it tries.
>> But as the kernel itself offers a sigsuspend() symbol the linker choose
>> this one instead of the glibc wrapper. Interestingly this code used to
>> work since ever but always blocked signals on the wrong side.
>> Some recent kernel change made the WARN_ON() trigger and uncovered the bug.
>>
> 
> So we don't know what caused this or when it started happening.  hrm. 
> I guess I'll stick a cc:stable in there as it's likely to affect 4.3
> and perhaps earlier, OK?

I fear it has been this way for ever.
CC'ing stable is a good idea!

Thanks,
//richard
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