mm/sparsemem: fix 'mem_section' will never be NULL gcc 12 warning
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 and adding an
explicit NR_SECTION_ROOTS check to make sure that there is no
out-of-bound array access.
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 3e347261a80b ("sparsemem extreme implementation")
Signed-off-by: Waiman Long <[email protected]>
Reported-by: Justin Forbes <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Rafael Aquini <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 962b14d..46ffab8 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1397,13 +1397,16 @@ static inline unsigned long *section_to_usemap(struct mem_section *ms)
static inline struct mem_section *__nr_to_section(unsigned long nr)
{
+ unsigned long root = SECTION_NR_TO_ROOT(nr);
+
+ if (unlikely(root >= NR_SECTION_ROOTS))
+ return NULL;
+
#ifdef CONFIG_SPARSEMEM_EXTREME
- if (!mem_section)
+ if (!mem_section || !mem_section[root])
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];
+ return &mem_section[root][nr & SECTION_ROOT_MASK];
}
extern size_t mem_section_usage_size(void);
