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([2405:201:682f:389d:c391:4ad4:fa2d:b790]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29034f8f9e0sm150546215ad.120.2025.10.13.22.06.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Oct 2025 22:06:21 -0700 (PDT) From: Deepanshu Kartikey To: muchun.song@linux.dev, osalvador@suse.de, david@redhat.com, akpm@linux-foundation.org, broonie@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com, Deepanshu Kartikey Subject: [PATCH v6] hugetlbfs: move lock assertions after early returns in huge_pmd_unshare() Date: Tue, 14 Oct 2025 10:36:09 +0530 Message-Id: <20251014050609.349461-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 Brow= n. A subsequent fix in commit 06e8ca1b3dca ("hugetlbfs: check for shareable lock before calling huge_pmd_unshare()") addressed this by checking __vma_shareable_lock() in the caller before calling huge_pmd_unshare(). However, a cleaner approach is to move the lock assertions in huge_pmd_unshare() itself to after the early return checks. The assertions are only needed when actual PMD unsharing work will be performed. If the function returns early because sz !=3D PMD_SIZE or the PMD is not shared, no locks are required. This patch removes the check added in commit 06e8ca1b3dca ("hugetlbfs: check for shareable lock before calling huge_pmd_unshare()") and instead moves the assertions inside huge_pmd_unshare(), keeping all the logic within the function itself. Reported-by: syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com Reported-by: Mark Brown Closes: https://syzkaller.appspot.com/bug?extid=3Df26d7c75c26ec19790e7 Fixes: dd83609b8898 ("hugetlbfs: skip VMAs without shareable locks in huget= lb_vmdelete_list") Suggested-by: David Hildenbrand Suggested-by: Oscar Salvador Tested-by: syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com Link: https://lore.kernel.org/mm-commits/20250925203504.7BE02C4CEF7@smtp.ke= rnel.org/ [v1] Link: https://lore.kernel.org/mm-commits/20250928185232.BEDB6C4CEF0@smtp.ke= rnel.org/ [v2] Link: https://lore.kernel.org/linux-mm/20251003174553.3078839-1-kartikey406= @gmail.com/ [v3] Link: https://lore.kernel.org/linux-mm/20251008052759.469714-1-kartikey406@= gmail.com/ [v4] Link: https://lore.kernel.org/linux-mm/CADhLXY72yEVDjXWfxBUXfXhNfb8MWqwJmcb= 1daEHmDeFW+DRGw@mail.gmail.com/ [v5] Signed-off-by: Deepanshu Kartikey --- Changes in v6: - Remove __vma_shareable_lock() check from __unmap_hugepage_range() that was added in v4 (commit 06e8ca1b3dca) - Move lock assertions after early returns in huge_pmd_unshare() - Complete implementation of David's cleaner approach Changes in v5: - Incomplete: only moved assertions, forgot to remove v4 check Changes in v4: - Check __vma_shareable_lock() in __unmap_hugepage_range() before calling huge_pmd_unshare() per Oscar's suggestion Changes in v3: - Add ZAP_FLAG_NO_UNSHARE to skip only PMD unsharing Changes in v2: - Skip entire VMAs without shareable locks (caused PUNCH_HOLE regression) Changes in v1: - Initial fix attempt --- mm/hugetlb.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 85b2dac79d25..0455119716ec 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5885,7 +5885,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, s= truct vm_area_struct *vma, } =20 ptl =3D huge_pte_lock(h, mm, ptep); - if (__vma_shareable_lock(vma) && huge_pmd_unshare(mm, vma, address, ptep= )) { + if (huge_pmd_unshare(mm, vma, address, ptep)) { spin_unlock(ptl); tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE); force_flush =3D true; @@ -7614,13 +7614,12 @@ int huge_pmd_unshare(struct mm_struct *mm, struct v= m_area_struct *vma, p4d_t *p4d =3D p4d_offset(pgd, addr); pud_t *pud =3D pud_offset(p4d, addr); =20 - i_mmap_assert_write_locked(vma->vm_file->f_mapping); - hugetlb_vma_assert_locked(vma); if (sz !=3D PMD_SIZE) return 0; if (!ptdesc_pmd_is_shared(virt_to_ptdesc(ptep))) return 0; - + i_mmap_assert_write_locked(vma->vm_file->f_mapping); + hugetlb_vma_assert_locked(vma); pud_clear(pud); /* * Once our caller drops the rmap lock, some other process might be --=20 2.34.1