linux-kernel - Re: [PATCH 2/4]percpu_counter: use correct API

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Date:	Wed, 13 Apr 2011 03:52:21 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, cl@...ux.com
Subject: Re: [PATCH 2/4]percpu_counter: use correct API

On Tue, Apr 12, 2011 at 04:04:01PM +0800, Shaohua Li wrote:
> percpu_counter_sum_positive never returns negative, since there
> is a negative check, I changed it to percpu_counter_sum.
> 
> Signed-off-by: Shaohua Li <shaohua.li@...el.com>
> 
> ---
>  fs/ext4/balloc.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux/fs/ext4/balloc.c
> ===================================================================
> --- linux.orig/fs/ext4/balloc.c	2011-04-12 15:48:42.000000000 +0800
> +++ linux/fs/ext4/balloc.c	2011-04-12 15:48:50.000000000 +0800
> @@ -506,7 +506,7 @@ static int ext4_has_free_blocks(struct e
>  	if (free_blocks - (nblocks + root_blocks + dirty_blocks) <
>  						EXT4_FREEBLOCKS_WATERMARK) {
>  		free_blocks  = percpu_counter_sum_positive(fbc);
> -		dirty_blocks = percpu_counter_sum_positive(dbc);
> +		dirty_blocks = percpu_counter_sum(dbc);
>  		if (dirty_blocks < 0) {
>  			printk(KERN_CRIT "Dirty block accounting "
>  					"went wrong %lld\n",

The right thing to do would be removing if (dirty_blocks < 0) and keep
using _positive.  perpcu_counter_sum() may return a negative number
spuriously (that's the whole point of _positive functions) and may
trigger the critial error path when nothing is really wrong.

Thanks.

-- 
tejun
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