linux-kernel - Re: [PATCH v3] kernel/signal.c: fix BUG

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Message-ID: <20130626161452.GA2888@redhat.com>
Date:	Wed, 26 Jun 2013 18:14:52 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	James Hogan <james.hogan@...tec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Daney <ddaney@...iumnetworks.com>,
	David Daney <ddaney.cavm@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Kees Cook <keescook@...omium.org>,
	David Daney <david.daney@...ium.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Dave Jones <davej@...hat.com>, linux-mips@...ux-mips.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v3] kernel/signal.c: fix BUG_ON with SIG128 (MIPS)

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@...tec.com>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: David Daney <david.daney@...ium.com>
> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Cc: David Howells <dhowells@...hat.com>
> Cc: Dave Jones <davej@...hat.com>
> Cc: linux-mips@...ux-mips.org
> Cc: stable@...r.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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