From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (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 7BD9023EAB4 for ; Wed, 15 Apr 2026 02:22:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776219770; cv=none; b=E6UNJRKUQE6RJvlacyiVhn+Wk3dm1Uyy6MG5rFCgQdWYrCT7VVIrpJ1qYBgheDj+KV/KBkbSIE1TRLEpZBOwUxnUbR1P+WCDzVca28umyaZX7MAKLaH04uon/Ib2vbEuFV8wwcvFAVJvyNmCsm2OzhRBiut/JBywmgZD0MDVabU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776219770; c=relaxed/simple; bh=jdSheN3HpBEtv6EP089OLg7gp2WBe8q9pFmRKgZtS8Q=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QwZhS0iqI2rznmaZmtt5s6CR/zvjn3phxK+5Wuav/GsRYOMh3Obu6GCb6PtNzffoH35pV6qmy189VISvWMkRER4MBf9N5nHbVypzGQFKzefWRW9PT3HP9Z2xhtQrz7euCNcVVCWHWrpBXP5Q8DItPzzZpXPygFLbV9/sAeDB1co= 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=IOjTynhS; arc=none smtp.client-ip=91.218.175.178 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="IOjTynhS" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1776219755; 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=SxdlTa6h3czNPKK/Gx4JCfQxJJmMB+PRQCNkrNojt5w=; b=IOjTynhSxRbXbBSIhYqt2yRd7gag1Ol6pIPFPPWfKEsMNn0st+gT7Nx2aN/4/2E9c0tByV o2/VyHreSZkVVP70OUwZcbozDNSPvno3Q4trUeesMZXyk/tXVVMWMlHl+WLb4/JQU3iAJb UrympiKJEuVbJBeZ/4t3uteVtAH3I6k= Date: Wed, 15 Apr 2026 10:22:05 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [syzbot] [mm?] [cgroups?] WARNING: bad unlock balance in lruvec_stat_mod_folio To: Shakeel Butt Cc: syzbot , akpm@linux-foundation.org, cgroups@vger.kernel.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, muchun.song@linux.dev, roman.gushchin@linux.dev, syzkaller-bugs@googlegroups.com, zhengqi.arch@bytedance.com, yosry@kernel.org References: <69d54494.050a0220.3030df.0002.GAE@google.com> <358c60e1-fa91-40a1-9e00-84c93340c04e@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 4/15/26 1:15 AM, Shakeel Butt wrote: > On Tue, Apr 14, 2026 at 11:52:13AM +0800, Qi Zheng wrote: >> Hi Shakeel, >> >> On 4/14/26 6:28 AM, Shakeel Butt wrote: >>> +Qi & Yosry >>> >>> On Tue, Apr 07, 2026 at 10:53:24AM -0700, syzbot wrote: >>>> Hello, >>>> >>>> syzbot found the following issue on: >>>> >>>> HEAD commit: cc13002a9f98 Add linux-next specific files for 20260402 >>>> git tree: linux-next >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=10d8946a580000 >>>> kernel config: https://syzkaller.appspot.com/x/.config?x=4e6c8be618ab359 >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=1a3353a77896e73a8f53 >>>> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 >>>> >>>> Unfortunately, I don't have any reproducer for this issue yet. >>> >>> Let's wait for the reproducer. I can only think of cgroup_subsys_on_dfl() check >>> returning different value in get_non_dying_memcg_start() and >>> get_non_dying_memcg_end() to cause this uneven rcu unlock. However I can't think >>> why and how that can happen. >>> >> >> My AI bot told me that the cgroup_subsys_on_dfl_key can be dynamically >> modified at runtime during a rebind: >> >> rebind_subsystems() >> --> if (dst_root == &cgrp_dfl_root) { >> static_branch_enable(cgroup_subsys_on_dfl_key[ssid]); >> } else { >> dcgrp->subtree_control |= 1 << ssid; >> static_branch_disable(cgroup_subsys_on_dfl_key[ssid]); >> } >> >> However, when I actually tested it, I hit the following error: >> >> mount: /tmp/cg-rb-repro: mount point is busy. >> >> Indeed, there are already many child cgroups under the cgroup v2 root >> (the VM just booted): >> >> root@localhost:~# find /sys/fs/cgroup -mindepth 1 -maxdepth 2 -type d | head >> -50 >> /sys/fs/cgroup/sys-kernel-debug.mount >> /sys/fs/cgroup/dev-mqueue.mount >> /sys/fs/cgroup/user.slice >> /sys/fs/cgroup/user.slice/user-0.slice >> /sys/fs/cgroup/sys-kernel-tracing.mount >> /sys/fs/cgroup/init.scope >> /sys/fs/cgroup/system.slice >> /sys/fs/cgroup/system.slice/systemd-networkd.service >> /sys/fs/cgroup/system.slice/systemd-udevd.service >> /sys/fs/cgroup/system.slice/system-serial\x2dgetty.slice >> /sys/fs/cgroup/system.slice/wpa_supplicant.service >> /sys/fs/cgroup/system.slice/system-modprobe.slice >> /sys/fs/cgroup/system.slice/systemd-journald.service >> /sys/fs/cgroup/system.slice/unattended-upgrades.service >> /sys/fs/cgroup/system.slice/system-systemd\x2dgrowfs.slice >> /sys/fs/cgroup/system.slice/ssh.service >> /sys/fs/cgroup/system.slice/dhcpcd.service >> /sys/fs/cgroup/system.slice/systemd-resolved.service >> /sys/fs/cgroup/system.slice/dbus.service >> /sys/fs/cgroup/system.slice/systemd-timesyncd.service >> /sys/fs/cgroup/system.slice/system-getty.slice >> /sys/fs/cgroup/system.slice/systemd-logind.service >> /sys/fs/cgroup/dev-hugepages.mount >> >> So it seems impossible to rebind memory in a production environment >> using systemd? >> >> Then I disabled systemd: >> >> set `init=/bin/bash` >> >> and found that I could successfully run the following commands: >> >> root@(none):/# mkdir -p /tmp/cg-rb-repro >> root@(none):/# mount -t cgroup -o none,name=rb none /tmp/cg-rb-repro >> root@(none):/# mount -t cgroup -o remount,memory none /tmp/cg-rb-repro >> [ 65.903125][ T241] option changes via remount are deprecated (pid=241 >> comm=mount) >> root@(none):/# mount -t cgroup -o remount,name=rb none /tmp/cg-rb-repro >> [ 73.405829][ T242] option changes via remount are deprecated (pid=242 >> comm=mount) >> root@(none):/# umount /tmp/cg-rb-repro >> >> So it seems this race condition does exist. Should we fix it? > > This only succeeded because there weren't any active cgroups. Were you able to > trigger the warning as well. If not, I think we should just wait for Nope. > reproducer from syzbot before doing anything. OK, Let's wait for syzbot to reproduce it. >