linux-kernel - Re: [PATCH] mm/zswap.c: add BUG() for default case in zswap_writeback

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Message-ID: <20131209153626.GA3752@cerebellum.variantweb.net>
Date:	Mon, 9 Dec 2013 09:36:26 -0600
From:	Seth Jennings <sjennings@...iantweb.net>
To:	Chen Gang <gang.chen.5i5j@...il.com>
Cc:	Seth Jennings <sjenning@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	James Hogan <james.hogan@...tec.com>
Subject: Re: [PATCH] mm/zswap.c: add BUG() for default case in
 zswap_writeback_entry()

On Mon, Dec 09, 2013 at 10:51:16AM +0800, Chen Gang wrote:
> Recommend to add default case to avoid compiler's warning, although at
> present, the original implementation is still correct.
> 
> The related warning (with allmodconfig for metag):
> 
>     CC      mm/zswap.o
>   mm/zswap.c: In function 'zswap_writeback_entry':
>   mm/zswap.c:537: warning: 'ret' may be used uninitialized in this function
> 
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
> ---
>  mm/zswap.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 5a63f78..bfd1807 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -585,6 +585,8 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle)
>  
>  		/* page is up to date */
>  		SetPageUptodate(page);
> +	default:
> +		BUG();

Typically, the way you want to address this is initialize ret to 0
at declaration time if not every control path will set that value.

Seth

>  	}
>  
>  	/* move it to the tail of the inactive list after end_writeback */
> -- 
> 1.7.7.6
> 
> --
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