Re: [akpm-mm:mm-unstable 25/274] mm/hugetlb.c:7281:3: error: call to undeclared function '__huge_pmd_unshare'; ISO C99 and later do not support implicit function declarations

[Lorenzo Stoakes <ljs@kernel.org>]

On Thu, May 14, 2026 at 04:37:45PM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-unstable
> head:   444fc9435e57157fcf30fc99aee44997f3458641
> commit: 2bb8fe16f7bf4487248c9ff847fcf189c45b9508 [25/274] mm/hugetlb: avoid false positive lockdep assertion
> config: powerpc64-randconfig-001-20260514 (https://download.01.org/0day-ci/archive/20260514/202605141638.b5ZBd6IF-lkp@intel.com/config)
> compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 5bac06718f502014fade905512f1d26d578a18f3)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260514/202605141638.b5ZBd6IF-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/202605141638.b5ZBd6IF-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
> >> mm/hugetlb.c:7281:3: error: call to undeclared function '__huge_pmd_unshare'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>     7281 |                 __huge_pmd_unshare(&tlb, vma, address, ptep, take_locks);
>          |                 ^
>    mm/hugetlb.c:7281:3: note: did you mean 'huge_pmd_unshare'?
>    mm/hugetlb.c:6973:5: note: 'huge_pmd_unshare' declared here
>     6973 | int huge_pmd_unshare(struct mmu_gather *tlb, struct vm_area_struct *vma,
>          |     ^
>    1 error generated.

Yup, I missed the !CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING case, sending a fix.

Cheers, Lorenzo

>
>
> vim +/__huge_pmd_unshare +7281 mm/hugetlb.c
>
>   7233
>   7234	/*
>   7235	 * If @take_locks is false, the caller must ensure that no concurrent page table
>   7236	 * access can happen (except for gup_fast() and hardware page walks).
>   7237	 * If @take_locks is true, we take the hugetlb VMA lock (to lock out things like
>   7238	 * concurrent page fault handling) and the file rmap lock.
>   7239	 */
>   7240	static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
>   7241					   unsigned long start,
>   7242					   unsigned long end,
>   7243					   bool take_locks)
>   7244	{
>   7245		struct hstate *h = hstate_vma(vma);
>   7246		unsigned long sz = huge_page_size(h);
>   7247		struct mm_struct *mm = vma->vm_mm;
>   7248		struct mmu_notifier_range range;
>   7249		struct mmu_gather tlb;
>   7250		unsigned long address;
>   7251		spinlock_t *ptl;
>   7252		pte_t *ptep;
>   7253
>   7254		if (!(vma->vm_flags & VM_MAYSHARE))
>   7255			return;
>   7256
>   7257		if (start >= end)
>   7258			return;
>   7259
>   7260		flush_cache_range(vma, start, end);
>   7261		tlb_gather_mmu_vma(&tlb, vma);
>   7262
>   7263		/*
>   7264		 * No need to call adjust_range_if_pmd_sharing_possible(), because
>   7265		 * we have already done the PUD_SIZE alignment.
>   7266		 */
>   7267		mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
>   7268					start, end);
>   7269		mmu_notifier_invalidate_range_start(&range);
>   7270		if (take_locks) {
>   7271			hugetlb_vma_lock_write(vma);
>   7272			i_mmap_lock_write(vma->vm_file->f_mapping);
>   7273		} else {
>   7274			i_mmap_assert_write_locked(vma->vm_file->f_mapping);
>   7275		}
>   7276		for (address = start; address < end; address += PUD_SIZE) {
>   7277			ptep = hugetlb_walk(vma, address, sz);
>   7278			if (!ptep)
>   7279				continue;
>   7280			ptl = huge_pte_lock(h, mm, ptep);
> > 7281			__huge_pmd_unshare(&tlb, vma, address, ptep, take_locks);
>   7282			spin_unlock(ptl);
>   7283		}
>   7284		huge_pmd_unshare_flush(&tlb, vma);
>   7285		if (take_locks) {
>   7286			i_mmap_unlock_write(vma->vm_file->f_mapping);
>   7287			hugetlb_vma_unlock_write(vma);
>   7288		}
>   7289		/*
>   7290		 * No need to call mmu_notifier_arch_invalidate_secondary_tlbs(), see
>   7291		 * Documentation/mm/mmu_notifier.rst.
>   7292		 */
>   7293		mmu_notifier_invalidate_range_end(&range);
>   7294		tlb_finish_mmu(&tlb);
>   7295	}
>   7296
>
> --
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