linux-kernel - Re: A regression in recent 3.2 kernel: bdi_dirty

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Message-ID: <1325954125.2442.27.camel@twins>
Date:	Sat, 07 Jan 2012 17:35:25 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Илья Тумайкин 
	<librarian_rus@...oo.com>, LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: A regression in recent 3.2 kernel: bdi_dirty_limit() divide
 error

On Sat, 2012-01-07 at 22:56 +0800, Wu Fengguang wrote:
> Subject: 
> Date: Sat Jan 07 22:50:45 CST 2012
> 
> The uninitilized shift may lead to denominator=0 in
> prop_fraction_percpu() and divide error in bdi_dirty_limit().

I'm not seeing how, only proc_change_shift() can change ->index, and it
does that after it writes ->pg[index]->shift.

> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  lib/proportions.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> --- linux.orig/lib/proportions.c        2012-01-07 22:50:29.000000000 +0800
> +++ linux/lib/proportions.c     2012-01-07 22:50:37.000000000 +0800
> @@ -82,6 +82,7 @@ int prop_descriptor_init(struct prop_des
>  
>         pd->index = 0;
>         pd->pg[0].shift = shift;
> +       pd->pg[1].shift = shift;
>         mutex_init(&pd->mutex);
>         err = percpu_counter_init(&pd->pg[0].events, 0);
>         if (err)
> 
> 
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