linux-kernel - Re: [PATCH] radix tree test suite: Fix uninitialized variable compilation warning

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Date:   Wed, 9 Nov 2022 16:23:48 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Rong Tao <rtoax@...mail.com>
Cc:     Rong Tao <rongtao@...tc.cn>, wuchi <wuchi.zero@...il.com>,
        linux-kernel@...r.kernel.org (open list), linux-mm@...ck.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] radix tree test suite: Fix uninitialized variable
 compilation warning

On Wed,  9 Nov 2022 22:34:25 +0800 Rong Tao <rtoax@...mail.com> wrote:

> [PATCH] radix tree test suite: Fix uninitialized variable compilation warning

This is not the test suite.

> We need to set an initial value for offset to eliminate compilation
> warning.
> 
> How to reproduce warning:
> 
> $ make -C tools/testing/radix-tree
> radix-tree.c: In function ‘radix_tree_tag_clear’:
> radix-tree.c:1046:17: warning: ‘offset’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>  1046 |                 node_tag_clear(root, parent, tag, offset);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> ...
>
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -1029,7 +1029,7 @@ void *radix_tree_tag_clear(struct radix_tree_root *root,
>  {
>  	struct radix_tree_node *node, *parent;
>  	unsigned long maxindex;
> -	int offset;
> +	int offset = 0;
>  
>  	radix_tree_load_root(root, &node, &maxindex);
>  	if (index > maxindex)

Are we sure this isn't actually a bug?  What happens if the tree is empty?