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Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)

To: James Hogan <james.hogan@imgtec.com>
Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)
From: Oleg Nesterov <oleg@redhat.com>
Date: Wed, 26 Jun 2013 18:14:52 +0200
Cc: Andrew Morton <akpm@linux-foundation.org>, David Daney <ddaney@caviumnetworks.com>, David Daney <ddaney.cavm@gmail.com>, LKML <linux-kernel@vger.kernel.org>, Ralf Baechle <ralf@linux-mips.org>, Al Viro <viro@zeniv.linux.org.uk>, Kees Cook <keescook@chromium.org>, David Daney <david.daney@cavium.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, David Howells <dhowells@redhat.com>, Dave Jones <davej@redhat.com>, linux-mips@linux-mips.org, stable@vger.kernel.org
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On 06/26, James Hogan wrote:
>
> On 25/06/13 23:13, James Hogan wrote:
>   BUG_ON(exit_code & 0x80); /* core dumps don't get here */
>
> As a quick fix, mask out higher bits in the signal number. This
> effectively matches the exit code from other code paths but avoids the
> BUG_ON.
> 
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: David Daney <david.daney@cavium.com>
> Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> Cc: David Howells <dhowells@redhat.com>
> Cc: Dave Jones <davej@redhat.com>
> Cc: linux-mips@linux-mips.org
> Cc: stable@vger.kernel.org
> ---
>  kernel/signal.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> 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);

Or simply remove the BUG_ON(), this can equally confuse wait(status).
128 & 0x7f == 0.

Still I think it would be better to change _NSIG on mips.

Oleg.


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