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 41CC93A8FEA for ; Tue, 21 Apr 2026 09:32:15 +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=1776763936; cv=none; b=S6KzMUzgJDka0bq0eGGL+KBHQqB43ob5u2b+I1klL7X22yefF0NyhJroyzqPZCEMATTc7n4ABvjXgMcYGGEUDLFUznCqsoqS6mbzNnyUgxhND9O+zazaEV5BTBAxiLN/w7XYLe13Rfpavur9c/WmQWzOjyLgik/vui+NTO9U9/Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776763936; c=relaxed/simple; bh=v8CjIjqWakQfGLJy9+I3WeWbMm2v1W7Fx6otO3HpYHw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qgBekFsIZ6z1sc6hsOEi2r8b3mRiPMsWNOY2MmxBSs91x5+Yl41WuDjOMkaZuc7K3UWVS3yr7JebrDNxkuNRGY8TLSBUQmHwVMpFPm+mAPYqUssztEkXQU7SFg4V/2Nj/Vpx1k/htjiTctx9TT6cywB2lRNCSFUsNciHxl52Xmc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lRbLeEEK; 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="lRbLeEEK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C6A9AC2BCB0; Tue, 21 Apr 2026 09:32:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776763934; bh=v8CjIjqWakQfGLJy9+I3WeWbMm2v1W7Fx6otO3HpYHw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=lRbLeEEKRZAxbka+gfmq9QRkcjZLBjw96VbSpNBsha8tZtlX2vwQVytNlaMzoPS7o PACQJXdLsLXVN+HKq53RvMN8MG8Wbh11XP7VtIPL0b17m2+fB4lAlnajH1eDKzWBFy apy/YwK4JAR0HfZo0zWtypU89V99HtFlp+NayRScj/WziyYG7BLg9IXfA/diuG0VDV 3ukIIlKmNVMVI+ouQGWwjAPyUE5nPnpjeGzY2vSxPMPuchf61ptfsIP9QRq1p9b20s qdw98/cBkwl111iKBz00MI76YUwlPmDwoo0pTAzcagzEFVbGbxV1SX/H8aKG0RVogM PH0fH21haLa3w== Date: Tue, 21 Apr 2026 10:32:10 +0100 From: Lorenzo Stoakes To: syzbot Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, jannh@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, pfalcato@suse.de, syzkaller-bugs@googlegroups.com, vbabka@kernel.org Subject: Re: [syzbot] [mm?] WARNING in vma_mark_detached Message-ID: References: <69e69734.050a0220.24bfd3.0027.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=us-ascii Content-Disposition: inline In-Reply-To: <69e69734.050a0220.24bfd3.0027.GAE@google.com> On Mon, Apr 20, 2026 at 02:14:28PM -0700, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 43cfbdda5af6 Merge tag 'for-linus-iommufd' of git://git.ke.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=17711906580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=8195c5b22e79c2cf > dashboard link: https://syzkaller.appspot.com/bug?extid=db390288d141a1dccf96 > 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=14cd78ce580000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=161f82d2580000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/848e46852283/disk-43cfbdda.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/24283dbdc318/vmlinux-43cfbdda.xz > kernel image: https://storage.googleapis.com/syzbot-assets/f91b3fadd31d/bzImage-43cfbdda.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+db390288d141a1dccf96@syzkaller.appspotmail.com > > RDX: bbdccba4532b703b RSI: 0000200000000000 RDI: 0000000000000000 > RBP: 00007ffcde93cf30 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 > R13: 00007fa5dec15fac R14: 00007fa5dec15fa0 R15: 00007fa5dec15fa0 > > HugeTLB: unable to allocate vma specific lock OK so this is the (sketchy) hugetlb 'VMA lock' allocation code, which in fact is not a VMA lock in the sense of core mm, but rather a hugetlb-specific thing. There is an alloc failiure injected to do that. > ------------[ cut here ]------------ > !vma_is_attached(vma) > WARNING: ./include/linux/mmap_lock.h:435 at vma_assert_attached include/linux/mmap_lock.h:435 [inline], CPU#0: syz.0.17/6011 > WARNING: ./include/linux/mmap_lock.h:435 at vma_mark_detached+0x198/0x260 include/linux/mmap_lock.h:455, CPU#0: syz.0.17/6011 But this is saying the VMA is detached, which shouldn't be the case... >From the below, we're in an mmap compatibility layer scenario, so this is complicated: shmat -> mmap_region -> shm_mmap -> compat_vma_mmap -> mmap_action_complete -> do_munmap -> vms_gather_munmap_vmas -> vma_mark_detached This then is a product of the VMA being in its incomplete, not-yet-initialised state, which explains why the VMA is detached. So I think we need a way of propagating to the mmap_action_finish() handler that we're in a compat handler and thus the unmapping is unnecessary. I'll come up with a patch! Cheers, Lorenzo > Modules linked in: > CPU: 0 UID: 0 PID: 6011 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026 > RIP: 0010:vma_assert_attached include/linux/mmap_lock.h:435 [inline] > RIP: 0010:vma_mark_detached+0x198/0x260 include/linux/mmap_lock.h:455 > Code: 01 00 00 00 89 ee e8 57 5f a4 ff 85 ed 7e 4b e8 0e 5b a4 ff 48 89 df 5b 41 5c 41 5e 41 5f 5d e9 7e db f3 ff e8 f9 5a a4 ff 90 <0f> 0b 90 eb 95 e8 ee 5a a4 ff 90 0f 0b 90 e9 04 ff ff ff e8 e0 5a > RSP: 0018:ffffc90003396df0 EFLAGS: 00010293 > RAX: ffffffff8220ba17 RBX: ffff8880536f8500 RCX: ffff88802baf3d80 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 > RBP: 0000000000000000 R08: ffff8880536f8583 R09: 1ffff1100a6df0b0 > R10: dffffc0000000000 R11: ffffed100a6df0b1 R12: dffffc0000000000 > R13: ffffc90003397130 R14: ffff8880536f8580 R15: 0000000000000001 > FS: 000055555c863500(0000) GS:ffff88812522b000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000001b2fb63fff CR3: 00000000325d8000 CR4: 00000000003526f0 > Call Trace: > > vms_gather_munmap_vmas+0x6ab/0x1380 mm/vma.c:1458 > do_vmi_align_munmap+0x2b4/0x4b0 mm/vma.c:1595 > do_vmi_munmap+0x252/0x2d0 mm/vma.c:1652 > do_munmap+0xf9/0x170 mm/mmap.c:1067 > mmap_action_finish mm/util.c:1422 [inline] > mmap_action_complete+0x480/0x590 mm/util.c:1491 > compat_vma_mmap+0x243/0x2c0 mm/util.c:1280 > vfs_mmap include/linux/fs.h:2072 [inline] > shm_mmap+0xda/0x200 ipc/shm.c:607 > vfs_mmap include/linux/fs.h:2074 [inline] > mmap_file mm/internal.h:168 [inline] > __mmap_new_file_vma mm/vma.c:2496 [inline] > __mmap_new_vma mm/vma.c:2562 [inline] > __mmap_region mm/vma.c:2771 [inline] > mmap_region+0x1ab2/0x2280 mm/vma.c:2856 > do_mmap+0xc39/0x10c0 mm/mmap.c:560 > do_shmat+0x8d8/0xc10 ipc/shm.c:1662 > __do_sys_shmat ipc/shm.c:1698 [inline] > __se_sys_shmat ipc/shm.c:1693 [inline] > __x64_sys_shmat+0x9c/0xf0 ipc/shm.c:1693 > 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: 0033:0x7fa5de99c819 > 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:00007ffcde93cec8 EFLAGS: 00000246 ORIG_RAX: 000000000000001e > RAX: ffffffffffffffda RBX: 00007fa5dec15fa0 RCX: 00007fa5de99c819 > RDX: bbdccba4532b703b RSI: 0000200000000000 RDI: 0000000000000000 > RBP: 00007ffcde93cf30 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 > R13: 00007fa5dec15fac R14: 00007fa5dec15fa0 R15: 00007fa5dec15fa0 > > > > --- > 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