The patch titled
Subject: mm/sparsemem: fix 'mem_section' will never be NULL gcc 12 warning
has been added to the -mm tree. Its filename is
mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch
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------------------------------------------------------
From: Waiman Long <longman@xxxxxxxxxx>
Subject: 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/20220331180246.2746210-1-longman@xxxxxxxxxx
Fixes: 3e347261a80b ("sparsemem extreme implementation")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Reported-by: Justin Forbes <jforbes@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mmzone.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
--- a/include/linux/mmzone.h~mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning
+++ a/include/linux/mmzone.h
@@ -1397,13 +1397,16 @@ static inline unsigned long *section_to_
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);
_
Patches currently in -mm which might be from longman@xxxxxxxxxx are
mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch
mm-list_lru-fix-possible-race-in-memcg_reparent_list_lru_node.patch
ipc-mqueue-use-get_tree_nodev-in-mqueue_get_tree.patch
