linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized

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Message-ID: <d1562b04-125f-c112-7272-d99ed1e38549@huawei.com>
Date:   Mon, 15 Jun 2020 16:26:25 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jason Yan <yanaijie@...wei.com>, <jaegeuk@...nel.org>,
        <chao@...nel.org>, <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
CC:     Kees Cook <keescook@...omium.org>,
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized_var()
 macro

On 2020/6/15 12:02, Jason Yan wrote:
> This is an effort to eliminate the uninitialized_var() macro[1].
> 
> The use of this macro is the wrong solution because it forces off ANY
> analysis by the compiler for a given variable. It even masks "unused
> variable" warnings.
> 
> Quoted from Linus[2]:
> 
> "It's a horrible thing to use, in that it adds extra cruft to the
> source code, and then shuts up a compiler warning (even the _reliable_
> warnings from gcc)."
> 
> The gcc option "-Wmaybe-uninitialized" has been disabled and this change
> will not produce any warnnings even with "make W=1".
> 
> [1] https://github.com/KSPP/linux/issues/81
> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> 
> Cc: Kees Cook <keescook@...omium.org>
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> ---
>  fs/f2fs/data.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 326c63879ddc..e6ec61274d76 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>  	};
>  #endif
>  	int nr_pages;
> -	pgoff_t uninitialized_var(writeback_index);
> +	pgoff_t writeback_index;

I suggest to delete this variable directly, as we did for mm in
commit 28659cc8cc87 (mm/page-writeback.c: remove unused variable).

Thanks,

>  	pgoff_t index;
>  	pgoff_t end;		/* Inclusive */
>  	pgoff_t done_index;
>