linux-kernel - Re: [PATCH 1/2] xfs: zero initialize highstale and lowstale in xfs_dir2_leaf

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Message-ID: <20190311164616.GA14469@archlinux-ryzen>
Date:   Mon, 11 Mar 2019 09:46:16 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH 1/2] xfs: zero initialize highstale and lowstale in
 xfs_dir2_leaf_addname

On Mon, Mar 11, 2019 at 09:19:48AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@...cle.com>
> 
> Smatch complains about the following:
> 
> fs/xfs/libxfs/xfs_dir2_leaf.c:848 xfs_dir2_leaf_addname() error:
> uninitialized symbol 'lowstale'.
> 
> fs/xfs/libxfs/xfs_dir2_leaf.c:849 xfs_dir2_leaf_addname() error:
> uninitialized symbol 'highstale'.
> 
> I don't think there's any incorrect behavior associated with the
> uninitialized variable, but as the author of the previous zero-init
> patch points out, it's best not to be passing around pointers to
> uninitialized stack areas.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>

Thanks for this!

> ---
>  fs/xfs/libxfs/xfs_dir2_leaf.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_dir2_leaf.c b/fs/xfs/libxfs/xfs_dir2_leaf.c
> index 9a3767818c50..2abf945e5844 100644
> --- a/fs/xfs/libxfs/xfs_dir2_leaf.c
> +++ b/fs/xfs/libxfs/xfs_dir2_leaf.c
> @@ -574,7 +574,7 @@ xfs_dir2_leaf_addname(
>  	xfs_dir2_data_unused_t	*dup;		/* data unused entry */
>  	int			error;		/* error return value */
>  	int			grown;		/* allocated new data block */
> -	int			highstale;	/* index of next stale leaf */
> +	int			highstale = 0;	/* index of next stale leaf */
>  	int			i;		/* temporary, index */
>  	int			index;		/* leaf table position */
>  	struct xfs_buf		*lbp;		/* leaf's buffer */
> @@ -583,7 +583,7 @@ xfs_dir2_leaf_addname(
>  	xfs_dir2_leaf_entry_t	*lep;		/* leaf entry table pointer */
>  	int			lfloglow;	/* low leaf logging index */
>  	int			lfloghigh;	/* high leaf logging index */
> -	int			lowstale;	/* index of prev stale leaf */
> +	int			lowstale = 0;	/* index of prev stale leaf */
>  	xfs_dir2_leaf_tail_t	*ltp;		/* leaf tail pointer */
>  	int			needbytes;	/* leaf block bytes needed */
>  	int			needlog;	/* need to log data header */