linux-kernel - Re: [RFC PATCH] kernel/signal.c: avoid BUG

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Message-ID: <CAAG0J9_yJd5mf0t7whnKDYtf0AdZDnErjOgUga7t0p3TEL_9YQ@mail.gmail.com>
Date:	Wed, 29 May 2013 22:56:44 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	David Daney <ddaney.cavm@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mips@...ux-mips.org,
	Ralf Baechle <ralf@...ux-mips.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	James Hogan <james.hogan@...tec.com>
Subject: Re: [RFC PATCH] kernel/signal.c: avoid BUG_ON with SIG128 (MIPS)

On 29 May 2013 18:36, Oleg Nesterov <oleg@...hat.com> wrote:
> On 05/29, David Daney wrote:
>>
>> On 05/29/2013 10:01 AM, James Hogan wrote:
>>> MIPS has 128 signals, the highest of which has the number 128. The
>>
>> I wonder if we should change the ABI and reduce the number of signals to
>> 127 instead of this patch.
>
> Same thoughts...

I'll give it a try. I wouldn't have thought it'd break anything, but
you never know. glibc (incorrectly) sets [__]SIGRTMAX to 127 already.
On the other hand uClibc sets it to 128, so anything built against
uClibc that uses signals SIGRTMAX-n (where n may be 0) or uses an
excessive number of rt signals starting from SIGRTMIN (sounds
unlikely) could well need an updated uClibc (or a full rebuild if it's
crazy enough to use __SIGRTMAX).

>>> @@ -2366,8 +2366,12 @@ relock:
>>>
>>>              /*
>>>               * Death signals, no core dump.
>>> +             *
>>> +             * MIPS has a signal number 128 which clashes with the core dump
>>> +             * bit. If this was the signal we still want to report a valid
>>> +             * exit code, so round it down to 127.
>>>               */
>>> -            do_group_exit(info->si_signo);
>>> +            do_group_exit(min(info->si_signo, 127));
>
> This avoids BUG_ON() but obviously fools WIFSIGNALED(), doesn't look
> very nice.

Agreed.

Cheers
James
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