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Date: Wed, 26 Jun 2013 18:01:12 +0200
From: Ralf Baechle <ralf@linux-mips.org>
To: James Hogan <james.hogan@imgtec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>,
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Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)
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On Wed, Jun 26, 2013 at 12:07:44PM +0100, James Hogan wrote:

> > IMO changing the ABI by reducing _NSIG to 127 or 126 isn't appropriate
> > for stable.
> 
> How does this look for a nasty/stable fix?

> diff --git a/kernel/signal.c b/kernel/signal.c
> index 113411b..9ea8f4f 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2366,8 +2366,14 @@ relock:
>  
>  		/*
>  		 * Death signals, no core dump.
> +		 *
> +		 * Some architectures (MIPS) have 128 signals which doesn't play
> +		 * nicely with the exit code since there are only 7 bits to
> +		 * store the terminating signal number. Mask out higher bits to
> +		 * avoid overflowing into the core dump bit and triggering
> +		 * BUG_ON in do_group_exit.
>  		 */
> -		do_group_exit(info->si_signo);
> +		do_group_exit(info->si_signo & 0x7f);
>  		/* NOTREACHED */
>  	}
>  	spin_unlock_irq(&sighand->siglock);

Looks like something which I think we could live with.

Clearly it also scores in the "nasty" category, so fits the bill ;)

  Ralf