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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 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 953D112000C X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: ibzyjeej6cw3musihrffpucbcg98t9en X-HE-Tag: 1760418383-649191 X-HE-Meta: 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 0zFgGuVO 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. 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 != 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=f26d7c75c26ec19790e7 Fixes: dd83609b8898 ("hugetlbfs: skip VMAs without shareable locks in hugetlb_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.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] Link: https://lore.kernel.org/linux-mm/20251008052759.469714-1-kartikey406@gmail.com/ [v4] Link: https://lore.kernel.org/linux-mm/CADhLXY72yEVDjXWfxBUXfXhNfb8MWqwJmcb1daEHmDeFW+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, struct vm_area_struct *vma, } ptl = 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 = true; @@ -7614,13 +7614,12 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, p4d_t *p4d = p4d_offset(pgd, addr); pud_t *pud = pud_offset(p4d, addr); - i_mmap_assert_write_locked(vma->vm_file->f_mapping); - hugetlb_vma_assert_locked(vma); if (sz != 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 -- 2.34.1