Re: [PATCH v2 5/7] mm: harden vma_count against direct modification

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

Hi Kalesh,

kernel test robot noticed the following build errors:

[auto build test ERROR on f83ec76bf285bea5727f478a68b894f5543ca76e]

url:    https://github.com/intel-lab-lkp/linux/commits/Kalesh-Singh/mm-fix-off-by-one-error-in-VMA-count-limit-checks/20250916-005018
base:   f83ec76bf285bea5727f478a68b894f5543ca76e
patch link:    https://lore.kernel.org/r/20250915163838.631445-6-kaleshsingh%40google.com
patch subject: [PATCH v2 5/7] mm: harden vma_count against direct modification
config: m68k-allnoconfig (https://download.01.org/0day-ci/archive/20250916/202509161708.EnaFVJbi-lkp@intel.com/config)
compiler: m68k-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250916/202509161708.EnaFVJbi-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/oe-kbuild-all/202509161708.EnaFVJbi-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/nommu.c: In function 'cleanup_vma_from_mm':
>> mm/nommu.c:579:30: error: decrement of read-only member 'vma_count'
     579 |         vma->vm_mm->vma_count--;
         |                              ^~
   mm/nommu.c: In function 'do_mmap':
>> mm/nommu.c:1201:31: error: increment of read-only member 'vma_count'
    1201 |         current->mm->vma_count++;
         |                               ^~
   mm/nommu.c: In function 'split_vma':
   mm/nommu.c:1369:22: error: increment of read-only member 'vma_count'
    1369 |         mm->vma_count++;
         |                      ^~


vim +/vma_count +579 mm/nommu.c

8220543df1489e Matthew Wilcox (Oracle  2022-09-06  576) 
8220543df1489e Matthew Wilcox (Oracle  2022-09-06  577) static void cleanup_vma_from_mm(struct vm_area_struct *vma)
8220543df1489e Matthew Wilcox (Oracle  2022-09-06  578) {
53045ecb29a61f Kalesh Singh            2025-09-15 @579  	vma->vm_mm->vma_count--;
^1da177e4c3f41 Linus Torvalds          2005-04-16  580  	/* remove the VMA from the mapping */
^1da177e4c3f41 Linus Torvalds          2005-04-16  581  	if (vma->vm_file) {
7964cf8caa4dfa Liam R. Howlett         2022-09-06  582  		struct address_space *mapping;
^1da177e4c3f41 Linus Torvalds          2005-04-16  583  		mapping = vma->vm_file->f_mapping;
^1da177e4c3f41 Linus Torvalds          2005-04-16  584  
83cde9e8ba95d1 Davidlohr Bueso         2014-12-12  585  		i_mmap_lock_write(mapping);
^1da177e4c3f41 Linus Torvalds          2005-04-16  586  		flush_dcache_mmap_lock(mapping);
6b2dbba8b6ac4d Michel Lespinasse       2012-10-08  587  		vma_interval_tree_remove(vma, &mapping->i_mmap);
^1da177e4c3f41 Linus Torvalds          2005-04-16  588  		flush_dcache_mmap_unlock(mapping);
83cde9e8ba95d1 Davidlohr Bueso         2014-12-12  589  		i_mmap_unlock_write(mapping);
^1da177e4c3f41 Linus Torvalds          2005-04-16  590  	}
8220543df1489e Matthew Wilcox (Oracle  2022-09-06  591) }
47d9644de92c1a Liam R. Howlett         2023-01-20  592  

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