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 9B47918991E; Fri, 22 Aug 2025 17:45:32 +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=1755884732; cv=none; b=n5JnBfzEli7vQqJTpdzauH/SFwCDWBAOkaRWXLR0c+j63tdFlJT9zv3vnawRPVMLZF1yvuA14wZUY1DnzbNNfuUQuxsVsdkPEDtGO+iAUowLSp+m47ALixEGvwtBzZgGeYobMzILcfw/2q7BZ9sg8Nutms7VaxdQm4C205gGte8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755884732; c=relaxed/simple; bh=2eHYpYgnRCw8iV3BbmM3JNNYiUhxphMW7B6RjWxwnM8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OJAB01QMHCJzsghtj9WOSx/hJ2hzAz9/zDbVWH4+wdXFm9w6Bm7Wp+V9JJXjSm13Rtk8lZpN511rRuPm/AQoZzpMoxqPktKdYCAiTslKNiYjE83nXl3HAl5zvqHqCpQK6bkgLCQVaAs8NnBknIAsZ+JmX6JC9oUd0bcYT0zsNFI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DGUs2K5G; 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="DGUs2K5G" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0983BC4CEED; Fri, 22 Aug 2025 17:45:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1755884732; bh=2eHYpYgnRCw8iV3BbmM3JNNYiUhxphMW7B6RjWxwnM8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DGUs2K5G/YF0rNqGKqHleGBu93TFnOQOrs3gbV/WpwfTj3+teaAUJRxEwdofjl8h2 hRvKStNS9kJamqBPoxorZbtBe0AQaOJWoY+id4t/+ckxZ9cuboGTCXPLILB5G++8HL w2weXPjHLNAOc9y3kDVYdkqQG/exbv2rGfN9nF5Pzx1HXMzYlMwajE5PaElG0MYtwf NwOwKXqhVN4tQ02jttflUDcNri0InaG0C5+D6gOGMKJj3KmPwVbJwnkXDYRUghsmNQ NPck804esG0W79ZvJW1IHApDVOAVRzVp1vj9wlCfpc/r4ZkeIQ8HkadTQCMF1NNOKT hqk3eNqhFxfxA== Date: Fri, 22 Aug 2025 07:45:31 -1000 From: Tejun Heo To: Chen Ridong Cc: hannes@cmpxchg.org, mkoutny@suse.com, lizefan@huawei.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, lujialin4@huawei.com, chenridong@huawei.com, hdanton@sina.com, gaoyingjie@uniontech.com Subject: Re: [PATCH v6] cgroup: split cgroup_destroy_wq into 3 workqueues Message-ID: References: <20250819010724.1338654-1-chenridong@huaweicloud.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250819010724.1338654-1-chenridong@huaweicloud.com> On Tue, Aug 19, 2025 at 01:07:24AM +0000, Chen Ridong wrote: > From: Chen Ridong > > A hung task can occur during [1] LTP cgroup testing when repeatedly > mounting/unmounting perf_event and net_prio controllers with > systemd.unified_cgroup_hierarchy=1. The hang manifests in > cgroup_lock_and_drain_offline() during root destruction. > > Related case: > cgroup_fj_function_perf_event cgroup_fj_function.sh perf_event > cgroup_fj_function_net_prio cgroup_fj_function.sh net_prio > > Call Trace: > cgroup_lock_and_drain_offline+0x14c/0x1e8 > cgroup_destroy_root+0x3c/0x2c0 > css_free_rwork_fn+0x248/0x338 > process_one_work+0x16c/0x3b8 > worker_thread+0x22c/0x3b0 > kthread+0xec/0x100 > ret_from_fork+0x10/0x20 > > Root Cause: > > CPU0 CPU1 > mount perf_event umount net_prio > cgroup1_get_tree cgroup_kill_sb > rebind_subsystems // root destruction enqueues > // cgroup_destroy_wq > // kill all perf_event css > // one perf_event css A is dying > // css A offline enqueues cgroup_destroy_wq > // root destruction will be executed first > css_free_rwork_fn > cgroup_destroy_root > cgroup_lock_and_drain_offline > // some perf descendants are dying > // cgroup_destroy_wq max_active = 1 > // waiting for css A to die > > Problem scenario: > 1. CPU0 mounts perf_event (rebind_subsystems) > 2. CPU1 unmounts net_prio (cgroup_kill_sb), queuing root destruction work > 3. A dying perf_event CSS gets queued for offline after root destruction > 4. Root destruction waits for offline completion, but offline work is > blocked behind root destruction in cgroup_destroy_wq (max_active=1) > > Solution: > Split cgroup_destroy_wq into three dedicated workqueues: > cgroup_offline_wq – Handles CSS offline operations > cgroup_release_wq – Manages resource release > cgroup_free_wq – Performs final memory deallocation > > This separation eliminates blocking in the CSS free path while waiting for > offline operations to complete. > > [1] https://github.com/linux-test-project/ltp/blob/master/runtest/controllers > Fixes: 334c3679ec4b ("cgroup: reimplement rebind_subsystems() using cgroup_apply_control() and friends") > Reported-by: Gao Yingjie > Signed-off-by: Chen Ridong > Suggested-by: Teju Heo Applied to cgroup/for-6.17-fixes. Sorry about the delay. I missed the thread. Thanks. -- tejun