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([2405:201:682f:389d:b33d:a221:52bf:8d99]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29034e18557sm161986165ad.39.2025.10.14.04.23.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Oct 2025 04:23:06 -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 v7] hugetlbfs: move lock assertions after early returns in huge_pmd_unshare() Date: Tue, 14 Oct 2025 16:52:56 +0530 Message-Id: <20251014112256.18793-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Stat-Signature: ab9dukbg3ugc4xbsc11x4p4a6woqre6w X-Rspam-User: X-Rspamd-Queue-Id: 3534A140003 X-HE-Tag: 1760440988-520939 X-HE-Meta: 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 Y58acH/B 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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. Instead of checking locks in the caller or skipping VMAs, move the lock assertions in huge_pmd_unshare() 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 and assertions should not fire. This is cleaner than previous approaches because it keeps all the logic within huge_pmd_unshare() itself, while still allowing page unmapping and freeing to proceed for all VMAs. 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] Link: https://lore.kernel.org/linux-mm/e6bb05f7-8f05-409f-9d87-2d25f66942a9@redhat.com/ [v6] Signed-off-by: Deepanshu Kartikey --- Changes in v7: - Rebased on mm/mm-stable per David's request - Move lock assertions after early returns in huge_pmd_unshare() Changes in v6: - Remove __vma_shareable_lock() check from __unmap_hugepage_range() - Move lock assertions after early returns in huge_pmd_unshare() 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 | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 795ee393eac0..0455119716ec 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -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