Re: [PATCH] mm/sparse: fix BUILD_BUG_ON check for section map alignment

[kernel test robot <lkp@intel.com>]

:::::: 
:::::: Manual check reason: "__compiletime_assert_NNN"
:::::: 

BCC: lkp@intel.com
CC: llvm@lists.linux.dev
CC: oe-kbuild-all@lists.linux.dev
In-Reply-To: <20260331113023.2068075-1-songmuchun@bytedance.com>
References: <20260331113023.2068075-1-songmuchun@bytedance.com>
TO: Muchun Song <songmuchun@bytedance.com>
TO: Andrew Morton <akpm@linux-foundation.org>
CC: Linux Memory Management List <linux-mm@kvack.org>
TO: David Hildenbrand <david@kernel.org>
CC: Lorenzo Stoakes <ljs@kernel.org>
CC: "Liam R. Howlett" <Liam.Howlett@oracle.com>
CC: Vlastimil Babka <vbabka@kernel.org>
CC: Mike Rapoport <rppt@kernel.org>
CC: Suren Baghdasaryan <surenb@google.com>
CC: Michal Hocko <mhocko@suse.com>
CC: Petr Tesarik <ptesarik@suse.com>
CC: linux-kernel@vger.kernel.org
CC: muchun.song@linux.dev
CC: Muchun Song <songmuchun@bytedance.com>

Hi Muchun,

kernel test robot noticed the following build errors:

[auto build test ERROR on linus/master]
[also build test ERROR on v7.0-rc6]
[cannot apply to akpm-mm/mm-everything next-20260401]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Muchun-Song/mm-sparse-fix-BUILD_BUG_ON-check-for-section-map-alignment/20260402-231649
base:   linus/master
patch link:    https://lore.kernel.org/r/20260331113023.2068075-1-songmuchun%40bytedance.com
patch subject: [PATCH] mm/sparse: fix BUILD_BUG_ON check for section map alignment
:::::: branch date: 11 hours ago
:::::: commit date: 11 hours ago
config: sparc64-defconfig (https://download.01.org/0day-ci/archive/20260403/202604031027.A6fEk4R5-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260403/202604031027.A6fEk4R5-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/r/202604031027.A6fEk4R5-lkp@intel.com/

All errors (new ones prefixed by >>):

>> mm/sparse.c:272:2: error: call to '__compiletime_assert_425' declared with 'error' attribute: BUILD_BUG_ON failed: SECTION_MAP_LAST_BIT > min(PFN_SECTION_SHIFT + __ffs(sizeof(struct page)), PAGE_SHIFT)
     272 |         BUILD_BUG_ON(SECTION_MAP_LAST_BIT > min(PFN_SECTION_SHIFT + __ffs(sizeof(struct page)),
         |         ^
   include/linux/build_bug.h:51:2: note: expanded from macro 'BUILD_BUG_ON'
      51 |         BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
         |         ^
   include/linux/build_bug.h:40:37: note: expanded from macro 'BUILD_BUG_ON_MSG'
      40 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
         |                                     ^
   include/linux/compiler_types.h:706:2: note: expanded from macro 'compiletime_assert'
     706 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
         |         ^
   include/linux/compiler_types.h:694:2: note: expanded from macro '_compiletime_assert'
     694 |         __compiletime_assert(condition, msg, prefix, suffix)
         |         ^
   include/linux/compiler_types.h:687:4: note: expanded from macro '__compiletime_assert'
     687 |                         prefix ## suffix();                             \
         |                         ^
   <scratch space>:216:1: note: expanded from here
     216 | __compiletime_assert_425
         | ^
   1 error generated.


vim +272 mm/sparse.c

9def36e0fa9a0d Logan Gunthorpe 2018-12-14  262  
29751f6991e845 Andy Whitcroft  2005-06-23  263  /*
29751f6991e845 Andy Whitcroft  2005-06-23  264   * Subtle, we encode the real pfn into the mem_map such that
29751f6991e845 Andy Whitcroft  2005-06-23  265   * the identity pfn - section_mem_map will return the actual
29751f6991e845 Andy Whitcroft  2005-06-23  266   * physical page frame number.
29751f6991e845 Andy Whitcroft  2005-06-23  267   */
29751f6991e845 Andy Whitcroft  2005-06-23  268  static unsigned long sparse_encode_mem_map(struct page *mem_map, unsigned long pnum)
29751f6991e845 Andy Whitcroft  2005-06-23  269  {
def9b71ee651a6 Petr Tesarik    2018-01-31  270  	unsigned long coded_mem_map =
def9b71ee651a6 Petr Tesarik    2018-01-31  271  		(unsigned long)(mem_map - (section_nr_to_pfn(pnum)));
d05a0da0a4e235 Muchun Song     2026-03-31 @272  	BUILD_BUG_ON(SECTION_MAP_LAST_BIT > min(PFN_SECTION_SHIFT + __ffs(sizeof(struct page)),
d05a0da0a4e235 Muchun Song     2026-03-31  273  						PAGE_SHIFT));
def9b71ee651a6 Petr Tesarik    2018-01-31  274  	BUG_ON(coded_mem_map & ~SECTION_MAP_MASK);
def9b71ee651a6 Petr Tesarik    2018-01-31  275  	return coded_mem_map;
29751f6991e845 Andy Whitcroft  2005-06-23  276  }
29751f6991e845 Andy Whitcroft  2005-06-23  277  

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