From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 BBEEC271A94 for ; Mon, 16 Feb 2026 14:40:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771252826; cv=none; b=jNYZe4D4qavU4SEfTFYZRCWlydXOqsopQ3p0sLYPf5D3ST5pBxyb27IaSocHYF9Tqhhd8E7ey10yEiMsMK2qlKvX+l4NM+wsTL0H61ekzjcL1lWJnBpAfzpPsXDR+xFTcdhTOu7MUPPELS/hX2lvAfKig6tyVMos/W3hU5sHl8w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771252826; c=relaxed/simple; bh=0dFHtqfSyLUzNUO7us0gUe1m4eQDoOg5I6BkTl63JDo=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=B15Rzlhn+y685xiObjz+yg44vHE/u5IadCUQDBUN7lj42bTEMjcGjxdmoaCBQkSkB4wr8Er9h0tcllhIybrjsStOFofGZ5VWn/m8dFvXDNv84kjngY6rv4qdNtDIe+Z5Zd+VHO2OjTIqTPHtbBYrZcpRBU9VHLvIcsFV5VSjFkk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NPccsK1E; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="NPccsK1E" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 21217C19423; Mon, 16 Feb 2026 14:40:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771252826; bh=0dFHtqfSyLUzNUO7us0gUe1m4eQDoOg5I6BkTl63JDo=; h=Date:Subject:To:References:From:In-Reply-To:From; b=NPccsK1EccekekdnMOc7lR5xjGsndNitrLnQZZ+4fL+2oar9yaJ6Lco+rrykkxm7I KvDHAKer8QEYodV6S7JG4PJO+8oJbAXNvgV06FfWDOrjFqZXOYdzRCoMDr1PTyDPDz CfO/RpHK8i2qH+p3WGRQJLcUVzNnNxGFhR7o0gPKDLpArBKi8k9iexqboMba1HOVsd cYkvsmgEqw3hKtK80u9Ce32wbz0pKa8NWAhjDXnpns73AIL67lsArpVZ9Kz4h+Z2jL MDMpX2NX86KLLfegQpMMN2cko6OTcl1ZcQnjIfg6c12kcY0jG76fYHCGUSeWOPgq0l 4082RPMfgnBkQ== Message-ID: <5e95c945-dbd4-4714-afb0-9546b08ff561@kernel.org> Date: Mon, 16 Feb 2026 15:40:21 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [mm?] kernel BUG in __khugepaged_enter To: syzbot , Liam.Howlett@oracle.com, akpm@linux-foundation.org, baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, lance.yang@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, npache@redhat.com, ryan.roberts@arm.com, syzkaller-bugs@googlegroups.com, ziy@nvidia.com References: <6990a57d.050a0220.2757fb.0028.GAE@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/14/26 17:40, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 1e83ccd5921a sched/mmcid: Don't assume CID is CPU owned on.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=1169dae6580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=54ae71b284dd0e13 > dashboard link: https://syzkaller.appspot.com/bug?extid=6b554d491efbe066b701 > compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/ed43f42e3ea1/disk-1e83ccd5.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/d8af54a32588/vmlinux-1e83ccd5.xz > kernel image: https://storage.googleapis.com/syzbot-assets/34e6a8cc1037/bzImage-1e83ccd5.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+6b554d491efbe066b701@syzkaller.appspotmail.com > > ------------[ cut here ]------------ > kernel BUG at mm/khugepaged.c:438! > Oops: invalid opcode: 0000 [#1] SMP KASAN PTI > CPU: 0 UID: 0 PID: 16472 Comm: syz.3.2372 Tainted: G U W L XTNJ syzkaller #0 PREEMPT(full) > Tainted: [U]=USER, [W]=WARN, [L]=SOFTLOCKUP, [X]=AUX, [T]=RANDSTRUCT, [N]=TEST, [J]=FWCTL > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026 > RIP: 0010:__khugepaged_enter+0x30a/0x380 mm/khugepaged.c:438 > Code: 64 7e 8e e8 a8 dc 66 ff e8 93 e6 8d ff 5b 5d 41 5c 41 5d 41 5e 41 5f e9 04 6c 04 09 e8 7f e6 8d ff 48 89 df e8 17 33 d9 ff 90 <0f> 0b 48 89 ef e8 dc 51 f8 ff e9 3b fd ff ff e8 f2 52 f8 ff e9 e1 > RSP: 0018:ffffc9000e98fba8 EFLAGS: 00010292 > RAX: 000000000000031f RBX: ffff888079b24980 RCX: 0000000000000000 > RDX: 000000000000031f RSI: ffffffff81e5b2c9 RDI: fffff52001d31f1c > RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000 > R10: 0000000080000000 R11: 0000000000000001 R12: 0000000008100177 > R13: ffff88804adf9510 R14: 0000000000000000 R15: 0000000000000000 > FS: 00007f06093436c0(0000) GS:ffff8881245b1000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fff341d3f52 CR3: 00000000319b0000 CR4: 00000000003526f0 > Call Trace: > > khugepaged_enter_vma mm/khugepaged.c:467 [inline] > khugepaged_enter_vma+0x137/0x2c0 mm/khugepaged.c:461 > do_huge_pmd_anonymous_page+0x1c8/0x1c00 mm/huge_memory.c:1469 > create_huge_pmd mm/memory.c:6102 [inline] > __handle_mm_fault+0x1e96/0x2b50 mm/memory.c:6376 > handle_mm_fault+0x36d/0xa20 mm/memory.c:6583 > do_user_addr_fault+0x5a3/0x12f0 arch/x86/mm/fault.c:1334 > handle_page_fault arch/x86/mm/fault.c:1474 [inline] > exc_page_fault+0x6f/0xd0 arch/x86/mm/fault.c:1527 > asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618 This is the VM_BUG_ON_MM(hpage_collapse_test_exit(mm), mm), which checks atomic_read(&mm->mm_users) == 0; So we have mm->mm_users == 0 while processing a page fault. Weird. -- Cheers, David