| From a431dbbc540532b7465eae4fc8b56a85a9fc7d17 Mon Sep 17 00:00:00 2001 |
| From: Waiman Long <longman@redhat.com> |
| Date: Fri, 8 Apr 2022 13:09:01 -0700 |
| Subject: mm/sparsemem: fix 'mem_section' will never be NULL gcc 12 warning |
| |
| 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); |
| |