When hugetlb_vmdelete_list() processes VMAs during truncate operations, it may encounter VMAs where huge_pmd_unshare() is called without the required shareable lock. This triggers an assertion failure in hugetlb_vma_assert_locked(). The previous fix in commit dd83609b8898 ("hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list") skipped entire VMAs without shareable locks to avoid the assertion. However, this prevented pages from being unmapped and freed, causing a regression in fallocate(PUNCH_HOLE) operations where pages were not freed immediately, as reported by Mark Brown. Instead of skipping VMAs or adding new flags, check __vma_shareable_lock() directly in __unmap_hugepage_range() right before calling huge_pmd_unshare(). This ensures PMD unsharing only happens when the VMA has a shareable lock structure, while still allowing page unmapping and freeing to proceed for all VMAs. Reported-by: syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com Tested-by: syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com Reported-by: Mark Brown Fixes: dd83609b8898 ("hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list") Suggested-by: Oscar Salvador Suggested-by: David Hildenbrand Link: https://lore.kernel.org/mm-commits/20250925203504.7BE02C4CEF7@smtp.kernel.org/ [v1] Link: https://lore.kernel.org/mm-commits/20250928185232.BEDB6C4CEF0@smtp.kernel.org/ [v2] Link: https://lore.kernel.org/linux-mm/20251003174553.3078839-1-kartikey406@gmail.com/ [v3] Signed-off-by: Deepanshu Kartikey --- Changes in v4: - Simplified approach per Oscar's suggestion: check __vma_shareable_lock() directly in __unmap_hugepage_range() before calling huge_pmd_unshare() - Removed ZAP_FLAG_NO_UNSHARE flag per David's feedback to avoid polluting generic mm.h header - Reverted hugetlb_vmdelete_list() to not skip VMAs Changes in v3: - Added ZAP_FLAG_NO_UNSHARE to skip only PMD unsharing, not entire VMA Changes in v2: - Skip entire VMAs without shareable locks in hugetlb_vmdelete_list() (caused PUNCH_HOLE regression) Changes in v1: - Initial fix attempt --- fs/hugetlbfs/inode.c | 10 +--------- mm/hugetlb.c | 2 +- 2 files changed, 2 insertions(+), 10 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 9c94ed8c3ab0..1e040db18b20 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -478,14 +478,6 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end, if (!hugetlb_vma_trylock_write(vma)) continue; - /* - * Skip VMAs without shareable locks. Per the design in commit - * 40549ba8f8e0, these will be handled by remove_inode_hugepages() - * called after this function with proper locking. - */ - if (!__vma_shareable_lock(vma)) - goto skip; - v_start = vma_offset_start(vma, start); v_end = vma_offset_end(vma, end); @@ -496,7 +488,7 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end, * vmas. Therefore, lock is not held when calling * unmap_hugepage_range for private vmas. */ -skip: + hugetlb_vma_unlock_write(vma); } } diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 6cac826cb61f..9ed85ab8420e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5885,7 +5885,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma, } ptl = huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, vma, address, ptep)) { + if (__vma_shareable_lock(vma) && huge_pmd_unshare(mm, vma, address, ptep)) { spin_unlock(ptl); tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE); force_flush = true; -- 2.43.0