Re: [PATCH v3 2/2] mm: Allocate THP on hugezeropage wp-fault

[kernel test robot]

Hi Dev,

kernel test robot noticed the following build warnings:

[auto build test WARNING on v6.11-rc7]
[also build test WARNING on linus/master]
[cannot apply to akpm-mm/mm-everything next-20240912]
[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/Dev-Jain/mm-Abstract-THP-allocation/20240911-145809
base:   v6.11-rc7
patch link:    https://lore.kernel.org/r/20240911065600.1002644-3-dev.jain%40arm.com
patch subject: [PATCH v3 2/2] mm: Allocate THP on hugezeropage wp-fault
config: x86_64-rhel-8.3-rust (https://download.01.org/0day-ci/archive/20240912/202409122349.PQp7sq2x-lkp@xxxxxxxxx/config)
compiler: clang version 18.1.8 (https://github.com/llvm/llvm-project 3b5b5c1ec4a3095ab096dd780e84d7ab81f3d7ff)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240912/202409122349.PQp7sq2x-lkp@xxxxxxxxx/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@xxxxxxxxx>
| Closes: https://lore.kernel.org/oe-kbuild-all/202409122349.PQp7sq2x-lkp@xxxxxxxxx/

All warnings (new ones prefixed by >>):

>> mm/huge_memory.c:990:15: warning: variable 'old_pmd' set but not used [-Wunused-but-set-variable]
     990 |         pmd_t entry, old_pmd;
         |                      ^
   mm/huge_memory.c:1016:6: warning: variable 'pgtable' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
    1016 |         if (unlikely(!folio)) {
         |             ^~~~~~~~~~~~~~~~
   include/linux/compiler.h:77:22: note: expanded from macro 'unlikely'
      77 | # define unlikely(x)    __builtin_expect(!!(x), 0)
         |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~
   mm/huge_memory.c:1055:6: note: uninitialized use occurs here
    1055 |         if (pgtable)
         |             ^~~~~~~
   mm/huge_memory.c:1016:2: note: remove the 'if' if its condition is always false
    1016 |         if (unlikely(!folio)) {
         |         ^~~~~~~~~~~~~~~~~~~~~~~
    1017 |                 ret = VM_FAULT_FALLBACK;
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~
    1018 |                 goto release;
         |                 ~~~~~~~~~~~~~
    1019 |         }
         |         ~
   mm/huge_memory.c:1010:19: note: initialize the variable 'pgtable' to silence this warning
    1010 |         pgtable_t pgtable;
         |                          ^
         |                           = NULL
   2 warnings generated.


vim +/old_pmd +990 mm/huge_memory.c

   986	
   987	static void map_pmd_thp(struct folio *folio, struct vm_fault *vmf,
   988				struct vm_area_struct *vma, unsigned long haddr)
   989	{
 > 990		pmd_t entry, old_pmd;
   991		bool is_pmd_none = pmd_none(*vmf->pmd);
   992	
   993		entry = mk_huge_pmd(&folio->page, vma->vm_page_prot);
   994		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
   995		folio_add_new_anon_rmap(folio, vma, haddr, RMAP_EXCLUSIVE);
   996		folio_add_lru_vma(folio, vma);
   997		if (!is_pmd_none)
   998			old_pmd = pmdp_huge_clear_flush(vma, haddr, vmf->pmd);
   999		set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
  1000		update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
  1001		add_mm_counter(vma->vm_mm, MM_ANONPAGES, HPAGE_PMD_NR);
  1002		if (is_pmd_none)
  1003			mm_inc_nr_ptes(vma->vm_mm);
  1004	}
  1005	

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