linux-kernel - Re: [PATCH -mm] signals-clear-signal-tty-when-the-last-thread-exits.fix

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Date:	Wed, 24 Mar 2010 07:41:49 -0400
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Alan Cox <alan@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm]
 signals-clear-signal-tty-when-the-last-thread-exits.fix

On Wed, 24 Mar 2010 15:23:48 +0100 Oleg Nesterov <oleg@...hat.com> wrote:

> (fixup for signals-clear-signal-tty-when-the-last-thread-exits.patch)
> 
> I didn't get this warning, but the old gcc complains
> 
> 	kernel/exit.c: In function 'release_task':
> 	kernel/exit.c:85: warning: 'tty' may be used uninitialized in this function
> 
> This clearly wrong, to the point it blames release_task() instead of
> __exit_signal(). But let's make compiler happy anyway, hopefully this
> is what it wants.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
> 
>  kernel/exit.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- 34-rc1/kernel/exit.c~FIX_EXIT_SIGNAL_TTY_WARNING	2010-03-21 18:36:44.000000000 +0100
> +++ 34-rc1/kernel/exit.c	2010-03-24 14:59:55.000000000 +0100
> @@ -82,7 +82,7 @@ static void __exit_signal(struct task_st
>  	struct signal_struct *sig = tsk->signal;
>  	bool group_dead = thread_group_leader(tsk);
>  	struct sighand_struct *sighand;
> -	struct tty_struct *tty;
> +	struct tty_struct *tty = NULL;	/* supress gcc warning */

uninitialized_var() is a neater way.

(uninitialized_var() will save a teeny bit of .text on old gcc.  One
suspects that a newer gcc which is capable of working out that this
variable _isn't_ uninitialized would also be capable of eliding the `= 0').

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