From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta1.migadu.com (out-171.mta1.migadu.com [95.215.58.171]) (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 3FF5318872A for ; Tue, 14 Apr 2026 03:52:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776138763; cv=none; b=YeNPZzirjxFCb1QUTIDeKSzk5Ur+HCa4/oxCTgyLpZV0vslLCzKHxmu0q5bGKu1CmkRI5mC1URRExJ7oXQH4xMQ6sNqhuYTjCkOCR0wbEgnHPFhOYzSDxM3JkCGmWBXBMqS+xQ95oDnIhWhLR1OJZUaKHcLCF9uCD8B9kRLBqJs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776138763; c=relaxed/simple; bh=mZJeyAghj1dS4ZD4LsG6V5nvwDifm0jZ5CqylaS6acc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=U/2w8NEGYcmgtjaVlJ8Vs5nsgJxt4cxbK5FuKDpDXYR18TF0PqWaNcod6YOZC4c4D3/V7NdMk6ZERFcFwepiXj6PnhfxzxesjOSqihM4DTFZLF4TkheDd4VeYQ4CnaCL8Xwt6giApK+aFu1d7yzJEllseHxfz+W8mXTpDsVHlzY= 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=LOdjCPmX; arc=none smtp.client-ip=95.215.58.171 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="LOdjCPmX" Message-ID: <358c60e1-fa91-40a1-9e00-84c93340c04e@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1776138754; 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=1Hsa5jfeTcTq/O2GmFxGJYQJNsRI2GpDuYxjEIeC86U=; b=LOdjCPmXff29fEJNKAZ3LMXkF9RzU2+hFU9CxpdNwutuqYVfL4ZInbe/sjUEEbqSDzBjEm IUNWxqVvNTpAwKQayHyG8BhbttLqSgBn6ACYfFMCMltOrO5EcHJcXCl7Z/bqIe3pL1t3SM cqKF6PtDYf93gaDyzuMiG0wScgL2eMY= Date: Tue, 14 Apr 2026 11:52:13 +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 , syzbot Cc: 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> 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 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? Thanks, Qi