Re: [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning

[Waiman Long <longman@redhat.com>]

On 2/1/22 14:29, Waiman Long wrote:
> The gcc 12 compiler reports a warning on the following code:
>
>      static inline struct mem_section *__nr_to_section(unsigned long nr)
>      {
>      #ifdef CONFIG_SPARSEMEM_EXTREME
>          if (!mem_section)
>                  return NULL;
>      #endif
>         :
>
> With CONFIG_SPARSEMEM_EXTREME on, the mem_section definition is
>
>      extern struct mem_section **mem_section;
>
> Obviously, mem_section cannot be NULL, but *mem_section can be if memory
> hasn't been allocated for the dynamic mem_section[] array yet. Fix this
> warning by checking for "!*mem_section" instead.
>
> Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")

Sorry, I forgot to add the line

Reported-by: Justin Forbes <jforbes@redhat.com>

> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>   include/linux/mmzone.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index aed44e9b5d89..bd1b19925f3b 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -1390,7 +1390,7 @@ static inline unsigned long *section_to_usemap(struct mem_section *ms)
>   static inline struct mem_section *__nr_to_section(unsigned long nr)
>   {
>   #ifdef CONFIG_SPARSEMEM_EXTREME
> -	if (!mem_section)
> +	if (!*mem_section)
>   		return NULL;
>   #endif
>   	if (!mem_section[SECTION_NR_TO_ROOT(nr)])