From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B8E9F223328 for ; Wed, 1 Apr 2026 08:10:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775031053; cv=none; b=Kh+xYVLEeCtCizJJK467MTkX7kTyyJZeUvvNiBRQ4+e0l0CpXbkGkLP7Jo5kVqofAMYpPcuY4BzZfyug64axDhbBa79FFew5JWi+Y6iguJGdUQNewSwXR6jPihLus4IJ/LLrTnxkenkFSshBpJkViXgWOUSu4MVApbeP2BzIBhk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775031053; c=relaxed/simple; bh=gkB+iS4i2034q2kIUo4513IQN1Ae1tsyu5WAYa9kBlg=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=V0PG+pYVPTwKjZokGcb/IMVPGxUR8cVQKKwckzwwtABpdCEknkybYvBGAYdt48nJwneFktW3IoXqBzHzHnWjyE3S2VPV4Dr4AqkRWQzWmxXv6kD38ZCGxrist2cWcE6kesML8Rf+084XwzmqzKwBA+WMxOEmpfEBrPA1p/Uij7g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=sMLGq1lB; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="sMLGq1lB" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775031045; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+MX+RoBiY5GwiGP2B5rBEJoBhjbFGz1wfvNFGjyXQdU=; b=sMLGq1lBOjKwNfxhwTIsTvcB2Yx/li/jpYvuuC6BF76iXh1NTBHs3zvmAYdxQQmznyGBLt 40k+kUzCzRxIg1JvfDNh73zhOK2DMY/jarvGN3WLZ5whjUHuYSasY89rIKrtZ9PKZzAbIg +kqut5ByqxmuDP4Ddnyw5f3CdH+3+ZQ= From: Lance Yang To: syzbot+a7067a757858ac8eb085@syzkaller.appspotmail.com, usama.arif@linux.dev Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, baohua@kernel.org, baolin.wang@linux.alibaba.com, david@kernel.org, dev.jain@arm.com, lance.yang@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, npache@redhat.com, ryan.roberts@arm.com, syzkaller-bugs@googlegroups.com, ziy@nvidia.com Subject: Re: [syzbot] [mm?] WARNING in deferred_split_folio Date: Wed, 1 Apr 2026 16:10:25 +0800 Message-Id: <20260401081025.68951-1-lance.yang@linux.dev> In-Reply-To: <69ccb65b.050a0220.183828.003a.GAE@google.com> References: <69ccb65b.050a0220.183828.003a.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT +Cc Usama On Tue, Mar 31, 2026 at 11:08:27PM -0700, syzbot wrote: >Hello, > >syzbot found the following issue on: > >HEAD commit: cf7c3c02fdd0 Add linux-next specific files for 20260330 >git tree: linux-next >console output: https://syzkaller.appspot.com/x/log.txt?x=154ee46a580000 >kernel config: https://syzkaller.appspot.com/x/.config?x=3944d875fa9bfb67 >dashboard link: https://syzkaller.appspot.com/bug?extid=a7067a757858ac8eb085 >compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 >syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12c846ba580000 > >Downloadable assets: >disk image: https://storage.googleapis.com/syzbot-assets/053d3b49a360/disk-cf7c3c02.raw.xz >vmlinux: https://storage.googleapis.com/syzbot-assets/faabb37d41d0/vmlinux-cf7c3c02.xz >kernel image: https://storage.googleapis.com/syzbot-assets/8d47fe92aaa8/bzImage-cf7c3c02.xz > >IMPORTANT: if you fix the issue, please add the following tag to the commit: >Reported-by: syzbot+a7067a757858ac8eb085@syzkaller.appspotmail.com > > free_pages_and_swap_cache+0x2b9/0x490 mm/swap_state.c:401 > __tlb_batch_free_encoded_pages mm/mmu_gather.c:138 [inline] > tlb_batch_pages_flush mm/mmu_gather.c:151 [inline] > tlb_flush_mmu_free mm/mmu_gather.c:417 [inline] > tlb_flush_mmu+0x6d3/0xa30 mm/mmu_gather.c:424 > tlb_finish_mmu+0xf9/0x230 mm/mmu_gather.c:549 > exit_mmap+0x498/0x9e0 mm/mmap.c:1313 > __mmput+0x118/0x430 kernel/fork.c:1177 > exit_mm+0x18e/0x250 kernel/exit.c:581 > do_exit+0x6a2/0x22c0 kernel/exit.c:962 > do_group_exit+0x21b/0x2d0 kernel/exit.c:1116 > __do_sys_exit_group kernel/exit.c:1127 [inline] > __se_sys_exit_group kernel/exit.c:1125 [inline] > __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1125 > x64_sys_call+0x221a/0x2240 arch/x86/include/generated/asm/syscalls_64.h:232 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f >------------[ cut here ]------------ >1 >WARNING: mm/huge_memory.c:4371 at deferred_split_folio+0x974/0xaa0 mm/huge_memory.c:4371, CPU#1: syz.3.1110/10500 >Modules linked in: >CPU: 1 UID: 0 PID: 10500 Comm: syz.3.1110 Not tainted syzkaller #0 PREEMPT(full) >Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026 >RIP: 0010:deferred_split_folio+0x974/0xaa0 mm/huge_memory.c:4371 >Code: 31 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f 5d e9 c2 67 8d 09 cc e8 8c 73 93 ff 48 89 df 48 c7 c6 20 5b fc 8b e8 dd 2b f5 fe 90 <0f> 0b 90 e9 d4 fe ff ff e8 9f 7a 8a 09 e8 6a 73 93 ff 48 89 df 48 >RSP: 0018:ffffc900047ef540 EFLAGS: 00010046 >RAX: 1c05fb65cfaab100 RBX: ffffea0001840000 RCX: 0000000080000001 >RDX: 0000000000000002 RSI: ffffffff8e4da1c7 RDI: ffff88807d6f9e80 >RBP: ffffc900047ef610 R08: ffff8880b87247d3 R09: 1ffff110170e48fa >R10: dffffc0000000000 R11: ffffed10170e48fb R12: ffffea0001840040 >R13: 0000000000000000 R14: 0000000000010000 R15: 1ffff920008fdeb0 >FS: 00007f32e32a76c0(0000) GS:ffff8881250e8000(0000) knlGS:0000000000000000 >CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >CR2: 00007f5825757930 CR3: 0000000034ad8000 CR4: 00000000003526f0 >Call Trace: > > migrate_folio_move mm/migrate.c:1411 [inline] Looks like a race introduced by commit[1] ("mm: migrate: requeue destination folio on deferred split queue"). Between folio migration (mbind) and rmap removal (exit_mmap), I guess :) migrate_folio_move() snapshots src_partially_mapped from src before migration: if (folio_order(src) > 1 && !data_race(list_empty(&src->_deferred_list))) { src_deferred_split = true; src_partially_mapped = folio_test_partially_mapped(src); } Then move_to_new_folio() eventually unqueues src in __folio_migrate_mapping(): folio_unqueue_deferred_split(src); After that, migration restores mappings to dst: if (old_page_state & PAGE_WAS_MAPPED) remove_migration_ptes(src, dst, 0); At that point, dst is already visible again. A concurrent unmap path from another sharer can then remove some of those mappings and reach deferred_split_folio(dst, true), which sets PG_partially_mapped on dst. Migration then resumes and does: if (src_deferred_split) deferred_split_folio(dst, src_partially_mapped); If the earlier snapshot from src was false, this becomes deferred_split_folio(dst, false), but dst may already have been marked partially mapped by the concurrent rmap-removal path, so the WARN in deferred_split_folio() fires: if (partially_mapped) { ... } else { /* partially mapped folios cannot become non-partially mapped */ VM_WARN_ON_FOLIO(folio_test_partially_mapped(folio), folio); } [1] https://lore.kernel.org/all/20260312104723.1351321-1-usama.arif@linux.dev/ > migrate_folios_move mm/migrate.c:1740 [inline] > migrate_pages_batch+0x319f/0x4c40 mm/migrate.c:1996 > migrate_pages_sync mm/migrate.c:2026 [inline] > migrate_pages+0x1c74/0x2a10 mm/migrate.c:2135 > do_mbind mm/mempolicy.c:1614 [inline] > kernel_mbind mm/mempolicy.c:1757 [inline] > __do_sys_mbind mm/mempolicy.c:1831 [inline] > __se_sys_mbind+0xe89/0x10f0 mm/mempolicy.c:1827 > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] > do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94 > entry_SYSCALL_64_after_hwframe+0x77/0x7f >RIP: 0033:0x7f32e239c819 >Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 >RSP: 002b:00007f32e32a7028 EFLAGS: 00000246 ORIG_RAX: 00000000000000ed >RAX: ffffffffffffffda RBX: 00007f32e2616090 RCX: 00007f32e239c819 >RDX: 0000000000000000 RSI: 0000000000800000 RDI: 0000200000001000 >RBP: 00007f32e2432c91 R08: 0000000000000000 R09: 0000000000000002 >R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 >R13: 00007f32e2616128 R14: 00007f32e2616090 R15: 00007ffe30c61cc8 > > > >--- >This report is generated by a bot. It may contain errors. >See https://goo.gl/tpsmEJ for more information about syzbot. >syzbot engineers can be reached at syzkaller@googlegroups.com. > >syzbot will keep track of this issue. See: >https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > >If the report is already addressed, let syzbot know by replying with: >#syz fix: exact-commit-title > >If you want syzbot to run the reproducer, reply with: >#syz test: git://repo/address.git branch-or-commit-hash >If you attach or paste a git patch, syzbot will apply it before testing. > >If you want to overwrite report's subsystems, reply with: >#syz set subsystems: new-subsystem >(See the list of subsystem names on the web dashboard) > >If the report is a duplicate of another one, reply with: >#syz dup: exact-subject-of-another-report > >If you want to undo deduplication, reply with: >#syz undup > >