linux-kernel - Re: [1/3] futex: fix compiler warnings in exit_robust

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Date:	Thu, 4 Nov 2010 11:49:12 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Darren Hart <dvhart@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org,
	Matt Fleming <matt@...sole-pimps.org>, tglx@...utronix.de,
	peterz@...radead.org, mingo@...e.hu, eric.dumazet@...il.com,
	jkacur@...hat.com
Subject: Re: [1/3] futex: fix compiler warnings in exit_robust_list

Hey Darren,

On Wed, Oct 27, 2010 at 09:54:24PM -0000, Darren Hart wrote:
> The following commit introduced a compiler warning:
> 
> Commit 1dcc41bb037533839753df983d31778b30b67d93
> futex: Change 3rd arg of fetch_robust_entry() to unsigned int*
> 
> The following archs/compiler versions all report:
> kernel/futex.c: In function ‘exit_robust_list’:
> kernel/futex.c:2492: warning: ‘next_pi’ may be used uninitialized in this function
> 
> x86_64
> gcc (Ubuntu 4.4.3-4ubuntu5) 4.4.3
> gcc (GCC) 4.4.4 20100630 (Red Hat 4.4.4-10)
> gcc (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5
> 
> sh
> sh-linux-gnu-gcc (Sourcery G++ Lite 4.3-143) 4.3.3
You can add

arm
arm-1136jfs-linux-gnueabi-gcc (OSELAS.Toolchain-1.99.3) 4.3.2

if you want.

> 
> The code path really can't result in next_pi pi being unitialized (or should
> not), but let's keep the build clean. Assign next_pi = 0 to avoid the warnings.
> 
> Signed-off-by: Darren Hart <dvhart@...ux.intel.com>
> Tested-by: Matt Fleming <matt@...sole-pimps.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> CC: Eric Dumazet <eric.dumazet@...il.com>
> CC: John Kacur <jkacur@...hat.com>
> 
> ---
> kernel/futex.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index a118bf1..78715cb 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -2489,7 +2489,7 @@ void exit_robust_list(struct task_struct *curr)
>  {
>  	struct robust_list_head __user *head = curr->robust_list;
>  	struct robust_list __user *entry, *next_entry, *pending;
> -	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
> +	unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi = 0, pip;
I'd prefer

+	unsigned int limit = ROBUST_LIST_LIMIT, pi, uninitialized_var(next_pi), pip;

(modulo line length).  This makes your change more explicit.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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