From: Waiman Long longman@redhat.com
commit a431dbbc540532b7465eae4fc8b56a85a9fc7d17 upstream.
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@redhat.com Fixes: 3e347261a80b ("sparsemem extreme implementation") Signed-off-by: Waiman Long longman@redhat.com Reported-by: Justin Forbes jforbes@redhat.com Cc: "Kirill A . Shutemov" kirill.shutemov@linux.intel.com Cc: Ingo Molnar mingo@kernel.org Cc: Rafael Aquini aquini@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/mmzone.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
--- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1389,13 +1389,16 @@ 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);