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

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

[Andrew Morton]

On Wed,  9 Nov 2022 22:34:25 +0800 Rong Tao <rtoax@foxmail.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?

[PATCH] lib/radix-tree: Fix uninitialized variable compilation warning

[Rong Tao]

From: Rong Tao <rongtao@cestc.cn>

We need to set an initial value for offset to eliminate compilation
warning. And if the tree is empty, return NULL early.

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);
     |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Rong Tao <rongtao@cestc.cn>
---
 lib/radix-tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 3c78e1e8b2ad..eee453b856b6 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -1029,10 +1029,10 @@ 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)
+	if (index > maxindex || !node)
 		return NULL;
 
 	parent = NULL;
-- 
2.31.1

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

[Matthew Wilcox]

On Wed, Nov 09, 2022 at 04:23:48PM -0800, Andrew Morton wrote:
> On Wed,  9 Nov 2022 22:34:25 +0800 Rong Tao <rtoax@foxmail.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?

If the tree is empty, then node is NULL and we never use offset.
The compiler is too stupid to know this.  This warning is only observed
when building the test suite and not when building the kernel itself.
I'm not sure the patch is worth it, tbh.

Re: [PATCH] lib/radix-tree: Fix uninitialized variable compilation warning

[Matthew Wilcox]

On Thu, Nov 10, 2022 at 01:00:42PM +0800, Rong Tao wrote:
>  	radix_tree_load_root(root, &node, &maxindex);
> -	if (index > maxindex)
> +	if (index > maxindex || !node)
>  		return NULL;

No, stop it, you don't know what you're doing.

Re: Re: [PATCH] lib/radix-tree: Fix uninitialized variable compilation warning

[Rong Tao]

Thanks for your reply, actually, at first time, i just want to fix the
compile warning, and i don't really know about the radix tree code,
i'm sorry, i hope i can do it better next time.

Rong Tao.