linux-kernel - Re: [PATCH v2] btrfs: Remove redundant assignment of slot and leaf

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Date:   Wed, 5 Jan 2022 16:11:30 +0000
From:   Filipe Manana <fdmanana@...nel.org>
To:     Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
Cc:     clm@...com, josef@...icpanda.com, dsterba@...e.com,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Abaci Robot <abaci@...ux.alibaba.com>
Subject: Re: [PATCH v2] btrfs: Remove redundant assignment of slot and leaf

On Wed, Jan 05, 2022 at 11:07:58PM +0800, Jiapeng Chong wrote:
> From: chongjiapeng <jiapeng.chong@...ux.alibaba.com>
> 
> slot and leaf are being initialized to path->slots[0] and
> path->nodes[0], but this is never read as slot and leaf
> is overwritten later on. Remove the redundant assignment.
> 
> Cleans up the following clang-analyzer warning:
> 
> fs/btrfs/tree-log.c:6125:7: warning: Value stored to 'slot' during its
> initialization is never read [clang-analyzer-deadcode.DeadStores].
> 
> Reported-by: Abaci Robot <abaci@...ux.alibaba.com>
> Signed-off-by: chongjiapeng <jiapeng.chong@...ux.alibaba.com>
> ---
> Changes in v2:
>   -Remove redundant assignment of leaf.
> 
>  fs/btrfs/tree-log.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index 4b89ac769347..d99cda0acd95 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -6188,8 +6188,6 @@ static int log_new_ancestors(struct btrfs_trans_handle *trans,
>  		if (ret < 0)
>  			return ret;
>  
> -		leaf = path->nodes[0];
> -		slot = path->slots[0];

No, this is not correct.

Right before those assignments we called btrfs_search_slot(), which updates
path->nodes and path->slots, and we need those updated values below.

The redundant assignments are not these two, but instead the ones when the
variables are declared at the top of the loop:

   struct extent_buffer *leaf = path->nodes[0];
   int slot = path->slots[0];

Thanks.

>  		if (slot >= btrfs_header_nritems(leaf)) {
>  			ret = btrfs_next_leaf(root, path);
>  			if (ret < 0)
> -- 
> 2.19.1.6.gb485710b
>