diff mbox series

[v3] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning

Message ID 20220330205919.2713275-1-longman@redhat.com (mailing list archive)
State New
Headers show
Series [v3] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning | expand

Commit Message

Waiman Long March 30, 2022, 8:59 p.m. UTC 
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(-)

Comments

kernel test robot March 31, 2022, 3:54 p.m. UTC | #1 
Hi Waiman,

I love your patch! Perhaps something to improve:

[auto build test WARNING on hnaz-mm/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Waiman-Long/mm-sparsemem-Fix-mem_section-will-never-be-NULL-gcc-12-warning/20220331-050049
base:   https://github.com/hnaz/linux-mm master
config: arm-randconfig-c024-20220330 (https://download.01.org/0day-ci/archive/20220331/202203312327.XGeCiD5T-lkp@intel.com/config)
compiler: arm-linux-gnueabi-gcc (GCC) 11.2.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/2098f1d78cde338e81b3ba596ea39f37824e496e
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Waiman-Long/mm-sparsemem-Fix-mem_section-will-never-be-NULL-gcc-12-warning/20220331-050049
        git checkout 2098f1d78cde338e81b3ba596ea39f37824e496e
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arm SHELL=/bin/bash security/keys/encrypted-keys/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from include/linux/gfp.h:6,
                    from include/linux/umh.h:4,
                    from include/linux/kmod.h:9,
                    from include/linux/module.h:17,
                    from security/keys/encrypted-keys/encrypted.c:15:
   security/keys/encrypted-keys/encrypted.c: In function 'derived_key_encrypt.constprop':
>> include/linux/mmzone.h:1432:23: warning: array subscript 32 is outside array bounds of 'struct mem_section[32][1]' [-Warray-bounds]
    1432 |         unsigned long map = section->section_mem_map;
         |                       ^~~
   include/linux/mmzone.h:1390:27: note: while referencing 'mem_section'
    1390 | extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
         |                           ^~~~~~~~~~~


vim +1432 include/linux/mmzone.h

29751f6991e845 Andy Whitcroft 2005-06-23  1429  
29751f6991e845 Andy Whitcroft 2005-06-23  1430  static inline struct page *__section_mem_map_addr(struct mem_section *section)
29751f6991e845 Andy Whitcroft 2005-06-23  1431  {
29751f6991e845 Andy Whitcroft 2005-06-23 @1432  	unsigned long map = section->section_mem_map;
29751f6991e845 Andy Whitcroft 2005-06-23  1433  	map &= SECTION_MAP_MASK;
29751f6991e845 Andy Whitcroft 2005-06-23  1434  	return (struct page *)map;
29751f6991e845 Andy Whitcroft 2005-06-23  1435  }
29751f6991e845 Andy Whitcroft 2005-06-23  1436
Waiman Long March 31, 2022, 4:05 p.m. UTC | #2 
On 3/31/22 11:54, kernel test robot wrote:
> Hi Waiman,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on hnaz-mm/master]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Waiman-Long/mm-sparsemem-Fix-mem_section-will-never-be-NULL-gcc-12-warning/20220331-050049
> base:   https://github.com/hnaz/linux-mm master
> config: arm-randconfig-c024-20220330 (https://download.01.org/0day-ci/archive/20220331/202203312327.XGeCiD5T-lkp@intel.com/config)
> compiler: arm-linux-gnueabi-gcc (GCC) 11.2.0
> reproduce (this is a W=1 build):
>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>          chmod +x ~/bin/make.cross
>          # https://github.com/intel-lab-lkp/linux/commit/2098f1d78cde338e81b3ba596ea39f37824e496e
>          git remote add linux-review https://github.com/intel-lab-lkp/linux
>          git fetch --no-tags linux-review Waiman-Long/mm-sparsemem-Fix-mem_section-will-never-be-NULL-gcc-12-warning/20220331-050049
>          git checkout 2098f1d78cde338e81b3ba596ea39f37824e496e
>          # save the config file to linux build tree
>          mkdir build_dir
>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arm SHELL=/bin/bash security/keys/encrypted-keys/
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
>     In file included from include/linux/gfp.h:6,
>                      from include/linux/umh.h:4,
>                      from include/linux/kmod.h:9,
>                      from include/linux/module.h:17,
>                      from security/keys/encrypted-keys/encrypted.c:15:
>     security/keys/encrypted-keys/encrypted.c: In function 'derived_key_encrypt.constprop':
>>> include/linux/mmzone.h:1432:23: warning: array subscript 32 is outside array bounds of 'struct mem_section[32][1]' [-Warray-bounds]
>      1432 |         unsigned long map = section->section_mem_map;
>           |                       ^~~
>     include/linux/mmzone.h:1390:27: note: while referencing 'mem_section'
>      1390 | extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
>           |                           ^~~~~~~~~~~
>
>
> vim +1432 include/linux/mmzone.h
>
> 29751f6991e845 Andy Whitcroft 2005-06-23  1429
> 29751f6991e845 Andy Whitcroft 2005-06-23  1430  static inline struct page *__section_mem_map_addr(struct mem_section *section)
> 29751f6991e845 Andy Whitcroft 2005-06-23  1431  {
> 29751f6991e845 Andy Whitcroft 2005-06-23 @1432  	unsigned long map = section->section_mem_map;
> 29751f6991e845 Andy Whitcroft 2005-06-23  1433  	map &= SECTION_MAP_MASK;
> 29751f6991e845 Andy Whitcroft 2005-06-23  1434  	return (struct page *)map;
> 29751f6991e845 Andy Whitcroft 2005-06-23  1435  }
> 29751f6991e845 Andy Whitcroft 2005-06-23  1436

I think this is a pre-existing warning. It is not caused by my patch, 
but I will take a look what cause the warning.

Thanks,
Longman
Waiman Long March 31, 2022, 5:33 p.m. UTC | #3 
On 3/31/22 11:54, kernel test robot wrote:
> Hi Waiman,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on hnaz-mm/master]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Waiman-Long/mm-sparsemem-Fix-mem_section-will-never-be-NULL-gcc-12-warning/20220331-050049
> base:   https://github.com/hnaz/linux-mm master
> config: arm-randconfig-c024-20220330 (https://download.01.org/0day-ci/archive/20220331/202203312327.XGeCiD5T-lkp@intel.com/config)
> compiler: arm-linux-gnueabi-gcc (GCC) 11.2.0
> reproduce (this is a W=1 build):
>          wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>          chmod +x ~/bin/make.cross
>          # https://github.com/intel-lab-lkp/linux/commit/2098f1d78cde338e81b3ba596ea39f37824e496e
>          git remote add linux-review https://github.com/intel-lab-lkp/linux
>          git fetch --no-tags linux-review Waiman-Long/mm-sparsemem-Fix-mem_section-will-never-be-NULL-gcc-12-warning/20220331-050049
>          git checkout 2098f1d78cde338e81b3ba596ea39f37824e496e
>          # save the config file to linux build tree
>          mkdir build_dir
>          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arm SHELL=/bin/bash security/keys/encrypted-keys/
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
>     In file included from include/linux/gfp.h:6,
>                      from include/linux/umh.h:4,
>                      from include/linux/kmod.h:9,
>                      from include/linux/module.h:17,
>                      from security/keys/encrypted-keys/encrypted.c:15:
>     security/keys/encrypted-keys/encrypted.c: In function 'derived_key_encrypt.constprop':
>>> include/linux/mmzone.h:1432:23: warning: array subscript 32 is outside array bounds of 'struct mem_section[32][1]' [-Warray-bounds]
>      1432 |         unsigned long map = section->section_mem_map;
>           |                       ^~~
>     include/linux/mmzone.h:1390:27: note: while referencing 'mem_section'
>      1390 | extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
>           |                           ^~~~~~~~~~~
>
>
> vim +1432 include/linux/mmzone.h
>
> 29751f6991e845 Andy Whitcroft 2005-06-23  1429
> 29751f6991e845 Andy Whitcroft 2005-06-23  1430  static inline struct page *__section_mem_map_addr(struct mem_section *section)
> 29751f6991e845 Andy Whitcroft 2005-06-23  1431  {
> 29751f6991e845 Andy Whitcroft 2005-06-23 @1432  	unsigned long map = section->section_mem_map;
> 29751f6991e845 Andy Whitcroft 2005-06-23  1433  	map &= SECTION_MAP_MASK;
> 29751f6991e845 Andy Whitcroft 2005-06-23  1434  	return (struct page *)map;
> 29751f6991e845 Andy Whitcroft 2005-06-23  1435  }
> 29751f6991e845 Andy Whitcroft 2005-06-23  1436
>
This warning happens with !CONFIG_SPARSEMEM_VMEMMAP && CONFIG_SPARSEMEM. 
In this case, __section_mem_map_addr() is used only by __pfn_to_page() 
and __page_to_pfn().  My patch only modifies __nr_to_section. In this 
particular case, it is removing The !mem_section[32] check. Perhaps it 
is somewhat equivalent to a (sec >= 32) check for gcc 11.2. However, 
this check will cause a warning in gcc 12. I will update the patch to 
add an explicit (sec >= NR_SECTION_ROOTS) then.

Thanks,
Longman
diff mbox series

Patch

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);