linux-kernel - Re: [PATCH] mm: cleanup balance_dirty_pages() that leave variables uninitialized

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Message-ID: <20151012125835.GD17050@quack.suse.cz>
Date:	Mon, 12 Oct 2015 14:58:35 +0200
From:	Jan Kara <jack@...e.cz>
To:	Liao Tonglang <liaotonglang@...il.com>
Cc:	tj@...nel.org, axboe@...com, akpm@...ux-foundation.org,
	jack@...e.cz, hannes@...xchg.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: cleanup balance_dirty_pages() that leave variables
 uninitialized

On Mon 12-10-15 20:24:58, Liao Tonglang wrote:
> Variables m_thresh and m_dirty in function balance_dirty_pages() may use
> uninitialized. GCC throws a warning on it. Fixed by assigned to 0 as
> initial value.

The code is correct - m_dirty & m_thresh gets set & used only if mdtc is
set. So the warning is false positive (and e.g. my gcc doesn't warn). What
gcc version are you using?

								Honza

> 
> Signed-off-by: Liao Tonglang <liaotonglang@...il.com>
> ---
>  mm/page-writeback.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 0a931cd..288db45 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1534,7 +1534,7 @@ static void balance_dirty_pages(struct address_space *mapping,
>  	for (;;) {
>  		unsigned long now = jiffies;
>  		unsigned long dirty, thresh, bg_thresh;
> -		unsigned long m_dirty, m_thresh, m_bg_thresh;
> +		unsigned long m_dirty = 0, m_thresh = 0, m_bg_thresh;
>  
>  		/*
>  		 * Unstable writes are a feature of certain networked
> -- 
> 1.8.3.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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