linux-kernel - Re: [PATCH] mm/zswap: Add return value in zswap_frontswap

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Date:   Fri, 22 Jan 2021 09:58:36 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     Nathan Chancellor <natechancellor@...il.com>
CC:     Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tian Tao <tiantao6@...ilicon.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        <clang-built-linux@...glegroups.com>,
        "kernelci . org bot" <bot@...nelci.org>,
        kernel test robot <lkp@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm/zswap: Add return value in zswap_frontswap_load

Hi:
On 2021/1/22 5:48, Nathan Chancellor wrote:
> Clang warns:
> 
> mm/zswap.c:1271:6: warning: variable 'ret' is used uninitialized
> whenever 'if' condition is true [-Wsometimes-uninitialized]
>         if (!entry->length) {
>             ^~~~~~~~~~~~~~
> mm/zswap.c:1322:9: note: uninitialized use occurs here
>         return ret;
>                ^~~
> mm/zswap.c:1271:2: note: remove the 'if' if its condition is always
> false
>         if (!entry->length) {
>         ^~~~~~~~~~~~~~~~~~~~~
> mm/zswap.c:1259:9: note: initialize the variable 'ret' to silence this
> warning
>         int ret;
>                ^
>                 = 0
> 1 warning generated.
> 
> Prior to "mm/zswap: add the flag can_sleep_mapped", this path always
> returned 0. Restore that so we are not returning uninitialized memory.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1263
> Reported-by: kernelci.org bot <bot@...nelci.org>
> Reported-by: kernel test robot <lkp@...el.com>

Looks like commit 6753c561f653 ("mm/zswap: add the flag can_sleep_mapped") introduced this warning.

> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> 
> Andrew, please fold this into
> 
> mm-zswap-add-the-flag-can_sleep_mapped.patch
> 
>  mm/zswap.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 6e0bb61d2a2c..a85334b719b9 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1272,6 +1272,7 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
>  		dst = kmap_atomic(page);
>  		zswap_fill_page(dst, entry->value);
>  		kunmap_atomic(dst);
> +		ret = 0;
>  		goto freeentry;
>  	}
>  
> 
> base-commit: bc085f8fc88fc16796c9f2364e2bfb3fef305cad
> 

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>