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98e67ed59e1d1-309f7de9616mr2520520a91.18.1745567306043; Fri, 25 Apr 2025 00:48:26 -0700 (PDT) Received: from KASONG-MC4.tencent.com ([43.132.141.20]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-309f77641eesm931158a91.25.2025.04.25.00.48.23 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Fri, 25 Apr 2025 00:48:25 -0700 (PDT) From: Kairui Song To: linux-mm@kvack.org Cc: Andrew Morton , David Hildenbrand , linux-kernel@vger.kernel.org, Kairui Song Subject: [PATCH] mm/memory: fix mapcount / refcount sanity check for mTHP reuse Date: Fri, 25 Apr 2025 15:43:25 +0800 Message-ID: <20250425074325.61833-1-ryncsn@gmail.com> X-Mailer: git-send-email 2.49.0 Reply-To: Kairui Song MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 81D85100002 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: b379sc4twzq39g7w7j58mjk1zzcndosf X-HE-Tag: 1745567307-271970 X-HE-Meta: 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 IQ4f3nW8 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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: From: Kairui Song The following WARNING was triggered during swap stress test with mTHP enabled: [ 6609.335758] ------------[ cut here ]------------ [ 6609.337758] WARNING: CPU: 82 PID: 755116 at mm/memory.c:3794 do_wp_page+0x1084/0x10e0 [ 6609.340922] Modules linked in: zram virtiofs [ 6609.342699] CPU: 82 UID: 0 PID: 755116 Comm: sh Kdump: loaded Not tainted 6.15.0-rc1+ #1429 PREEMPT(voluntary) [ 6609.347620] Hardware name: Red Hat KVM/RHEL-AV, BIOS 0.0.0 02/06/2015 [ 6609.349909] RIP: 0010:do_wp_page+0x1084/0x10e0 [ 6609.351532] Code: ff ff 48 c7 c6 80 ba 49 82 4c 89 ef e8 95 fd fe ff 0f 0b bd f5 ff ff ff e9 43 fb ff ff 41 83 a9 bc 12 00 00 01 e9 5c fb ff ff <0f> 0b e9 a6 fc ff ff 65 ff 00 f0 48 0f b a 6d 00 1f 0f 83 82 fc ff [ 6609.357959] RSP: 0000:ffffc90002273d40 EFLAGS: 00010287 [ 6609.359915] RAX: 000000000000000f RBX: 0000000000000000 RCX: 000fffffffe00000 [ 6609.362606] RDX: 0000000000000010 RSI: 000055a119ac1000 RDI: ffffea000ae6ec00 [ 6609.365143] RBP: ffffea000ae6ec68 R08: 84000002b9bb1025 R09: 000055a119ab6000 [ 6609.367569] R10: ffff8881caa2ad80 R11: 0000000000000000 R12: ffff8881caa2ad80 [ 6609.370255] R13: ffffea000ae6ec00 R14: 000055a119ac1c9c R15: ffffc90002273dd8 [ 6609.373007] FS: 00007f08e467f740(0000) GS:ffff88a07c214000(0000) knlGS:0000000000000000 [ 6609.375999] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 6609.377946] CR2: 000055a119ac1c9c CR3: 00000001adfd6005 CR4: 0000000000770eb0 [ 6609.380376] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 6609.382853] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 6609.385216] PKRU: 55555554 [ 6609.386141] Call Trace: [ 6609.387017] [ 6609.387718] ? ___pte_offset_map+0x1b/0x110 [ 6609.389056] __handle_mm_fault+0xa51/0xf00 [ 6609.390363] ? exc_page_fault+0x6a/0x140 [ 6609.391629] handle_mm_fault+0x13d/0x360 [ 6609.392856] do_user_addr_fault+0x2f2/0x7f0 [ 6609.394160] ? sigprocmask+0x77/0xa0 [ 6609.395375] exc_page_fault+0x6a/0x140 [ 6609.396735] asm_exc_page_fault+0x26/0x30 [ 6609.398224] RIP: 0033:0x55a1050bc18b [ 6609.399567] Code: 8b 3f 4d 85 ff 74 40 41 39 5f 18 75 f2 49 8b 7f 08 44 38 27 75 e9 4c 89 c6 4c 89 45 c8 e8 bd 83 fa ff 4c 8b 45 c8 85 c0 75 d5 <41> 83 47 1c 01 48 83 c4 28 4c 89 f8 5b 4 1 5c 41 5d 41 5e 41 5f 5d [ 6609.405971] RSP: 002b:00007ffcf5f37d90 EFLAGS: 00010246 [ 6609.407737] RAX: 0000000000000000 RBX: 00000000182768fa RCX: 0000000000000000 [ 6609.410151] RDX: 00000000000000fa RSI: 000055a105175c7b RDI: 000055a119ac1c60 [ 6609.412606] RBP: 00007ffcf5f37de0 R08: 000055a105175c7b R09: 0000000000000000 [ 6609.414998] R10: 000000004d2dfb5a R11: 0000000000000246 R12: 0000000000000050 [ 6609.417193] R13: 00000000000000fa R14: 000055a119abaf60 R15: 000055a119ac1c80 [ 6609.419268] [ 6609.419928] ---[ end trace 0000000000000000 ]--- The WARN_ON here is simply incorrect. The refcount here must be at least the mapcount, not the opposite. Each mapcount must have a corresponding refcount, but the refcount may increase if other components grab the folio, which is acceptable. Meanwhile, having a mapcount larger than refcount is a real problem. So fix the WARN_ON condition. Fixes: 1da190f4d0a6 ("mm: Copy-on-Write (COW) reuse support for PTE-mapped THP") Reported-by: Kairui Song Closes: https://lore.kernel.org/all/CAMgjq7D+ea3eg9gRCVvRnto3Sv3_H3WVhupX4e=k8T5QAfBHbw@mail.gmail.com/ Suggested-by: David Hildenbrand Signed-off-by: Kairui Song --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index 424420349bd3..f18266b5a0a9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3789,7 +3789,7 @@ static bool __wp_can_reuse_large_anon_folio(struct folio *folio, /* Stabilize the mapcount vs. refcount and recheck. */ folio_lock_large_mapcount(folio); - VM_WARN_ON_ONCE(folio_large_mapcount(folio) < folio_ref_count(folio)); + VM_WARN_ON_ONCE_FOLIO(folio_large_mapcount(folio) > folio_ref_count(folio), folio); if (folio_test_large_maybe_mapped_shared(folio)) goto unlock; -- 2.49.0