Re: [PATCH v3 1/2] mm: Abstract THP allocation

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

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/20240911065600.1002644-2-dev.jain%40arm.com
patch subject: [PATCH v3 1/2] mm: Abstract THP allocation
config: x86_64-rhel-8.3-rust (https://download.01.org/0day-ci/archive/20240912/202409122144.jqe4JROY-lkp@intel.com/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/20240912/202409122144.jqe4JROY-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/202409122144.jqe4JROY-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> mm/huge_memory.c:1012:6: warning: variable 'pgtable' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
    1012 |         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:1051:6: note: uninitialized use occurs here
    1051 |         if (pgtable)
         |             ^~~~~~~
   mm/huge_memory.c:1012:2: note: remove the 'if' if its condition is always false
    1012 |         if (unlikely(!folio)) {
         |         ^~~~~~~~~~~~~~~~~~~~~~~
    1013 |                 ret = VM_FAULT_FALLBACK;
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~
    1014 |                 goto release;
         |                 ~~~~~~~~~~~~~
    1015 |         }
         |         ~
   mm/huge_memory.c:1006:19: note: initialize the variable 'pgtable' to silence this warning
    1006 |         pgtable_t pgtable;
         |                          ^
         |                           = NULL
   1 warning generated.


vim +1012 mm/huge_memory.c

  1001	
  1002	static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf)
  1003	{
  1004		struct vm_area_struct *vma = vmf->vma;
  1005		struct folio *folio;
  1006		pgtable_t pgtable;
  1007		unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
  1008		vm_fault_t ret = 0;
  1009		gfp_t gfp = vma_thp_gfp_mask(vma);
  1010	
  1011		folio = pmd_thp_fault_alloc(gfp, vma, haddr, vmf->address);
> 1012		if (unlikely(!folio)) {
  1013			ret = VM_FAULT_FALLBACK;
  1014			goto release;
  1015		}
  1016	
  1017		pgtable = pte_alloc_one(vma->vm_mm);
  1018		if (unlikely(!pgtable)) {
  1019			ret = VM_FAULT_OOM;
  1020			goto release;
  1021		}
  1022	
  1023		vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
  1024	
  1025		if (unlikely(!pmd_none(*vmf->pmd))) {
  1026			goto unlock_release;
  1027		} else {
  1028			ret = check_stable_address_space(vma->vm_mm);
  1029			if (ret)
  1030				goto unlock_release;
  1031	
  1032			/* Deliver the page fault to userland */
  1033			if (userfaultfd_missing(vma)) {
  1034				spin_unlock(vmf->ptl);
  1035				folio_put(folio);
  1036				pte_free(vma->vm_mm, pgtable);
  1037				ret = handle_userfault(vmf, VM_UFFD_MISSING);
  1038				VM_BUG_ON(ret & VM_FAULT_FALLBACK);
  1039				return ret;
  1040			}
  1041			pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
  1042			map_pmd_thp(folio, vmf, vma, haddr);
  1043			spin_unlock(vmf->ptl);
  1044			__pmd_thp_fault_success_stats(vma);
  1045		}
  1046	
  1047		return 0;
  1048	unlock_release:
  1049		spin_unlock(vmf->ptl);
  1050	release:
  1051		if (pgtable)
  1052			pte_free(vma->vm_mm, pgtable);
  1053		if (folio)
  1054			folio_put(folio);
  1055		return ret;
  1056	

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