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Subject[PATCH v3] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning
Date
The gcc 12 compiler reports a "'mem_section' will never be NULL"
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
if (!mem_section[SECTION_NR_TO_ROOT(nr)])
return NULL;
:

It happens with CONFIG_SPARSEMEM_EXTREME off. The mem_section
definition is

#ifdef CONFIG_SPARSEMEM_EXTREME
extern struct mem_section **mem_section;
#else
extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
#endif

In the !CONFIG_SPARSEMEM_EXTREME case, mem_section
is a static 2-dimensional array and so the check
"!mem_section[SECTION_NR_TO_ROOT(nr)]" doesn't make sense.

Fix this warning by moving the "!mem_section[SECTION_NR_TO_ROOT(nr)]"
check up inside the CONFIG_SPARSEMEM_EXTREME block.

Fixes: 3e347261a80b ("sparsemem extreme implementation")
Reported-by: Justin Forbes <jforbes@redhat.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
include/linux/mmzone.h | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 962b14d403e8..8a89efe47571 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1398,11 +1398,9 @@ 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 || !mem_section[SECTION_NR_TO_ROOT(nr)])
return NULL;
#endif
- if (!mem_section[SECTION_NR_TO_ROOT(nr)])
- return NULL;
return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
}
extern size_t mem_section_usage_size(void);
--
2.27.0
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