From patchwork Mon Apr 4 14:25:34 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bui Quang Minh X-Patchwork-Id: 12800282 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CE325C433EF for ; Mon, 4 Apr 2022 14:26:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377148AbiDDO14 (ORCPT ); Mon, 4 Apr 2022 10:27:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377120AbiDDO1v (ORCPT ); Mon, 4 Apr 2022 10:27:51 -0400 Received: from mail-pf1-x42a.google.com (mail-pf1-x42a.google.com [IPv6:2607:f8b0:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 597DC3A1A0; Mon, 4 Apr 2022 07:25:55 -0700 (PDT) Received: by mail-pf1-x42a.google.com with SMTP id p8so9110422pfh.8; Mon, 04 Apr 2022 07:25:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=vmv5bxS5EWoc91g75Vzau8g0vSoXhGCuFE3qsoGJOPg=; b=iLoswEs+5gduzsNqGbxzYOyUkRa1X0c3WNYv/u/uht/PCXO/BiXTGor+UATG1GTo6y OGELiV1powqWayUslDrEskMHNAl8PdUCe3zrYMGuEpjb0SG651wSIW5wM/UIDfb1PZgG 2rCDyu3AADU/NXP0STTiWOZLLWHV7uRWxj+y4sOtv8PjerEPhadRF4w7GqVI3QXUtwqF bT+ra2vKQE0gYitrlGR5MiR6O1XfsTD3MI/2xGVGgnZj5a6qadtKTICBPaJnRhNLfB6/ KUa4yk9AVOzRKckxcSezhAXhgEsJxuzfcI//tqd5HH0z8FsYQsPKw3YQbEIvpxmwDwOP JVeA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=vmv5bxS5EWoc91g75Vzau8g0vSoXhGCuFE3qsoGJOPg=; b=h3kDDe+C0tfmZY9ZeOBQ1wNVWZcrh+JlZp51Lhyclbwoy42iGep3mvKQWu7wycIOdS i7CyrS6jDXEc+v5EesJwawznVeXrMqaGLG4GqQvxIVQxIH2YuucVGt/f+PVbDK6Xwy+z 0aHYBVl5EDsOmfBiKKZWL1UwSMaTYge7uQKJyp5yeuH5TAuxM519uFNPihqaUTiI3utd X1slxyEVB6gELKer13AykGZKBpX//Uyn3KaBbt/R9hFFhSHu6M368F9vUj5DkFkVCRS2 BuIqt8xMwhu864jFSyS7wjbgExk6wkdVTn0HTfY9DBWOSisxbJdHld4lCstrmaF5j4W7 o1/A== X-Gm-Message-State: AOAM532an8Oqzu+OEq71kQRIfW1fv9it8a1sxQ4eHYyMdswQEXSg0hqR 8L31s2JAlVIEPjau0FGfcI+iENF6NSlsmOi9 X-Google-Smtp-Source: ABdhPJwafKw9Rd90yVwt4IwWyyjMnWg7+ojtxRE2EoMZ3MPJVS4w/Y1rqKQlSraUbOO5P0FoxajaCg== X-Received: by 2002:a05:6a00:10c2:b0:4fd:a140:d5a9 with SMTP id d2-20020a056a0010c200b004fda140d5a9mr238623pfu.77.1649082354570; Mon, 04 Apr 2022 07:25:54 -0700 (PDT) Received: from localhost.localdomain ([113.173.105.8]) by smtp.googlemail.com with ESMTPSA id p3-20020a056a000b4300b004faee36ea56sm12731625pfo.155.2022.04.04.07.25.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Apr 2022 07:25:54 -0700 (PDT) From: Bui Quang Minh To: cgroups@vger.kernel.org Cc: Bui Quang Minh , kernel test robot , Tejun Heo , Zefan Li , Johannes Weiner , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: [PATCH v2] cgroup: Kill the parent controller when its last child is killed Date: Mon, 4 Apr 2022 21:25:34 +0700 Message-Id: <20220404142535.145975-1-minhquangbui99@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org When umounting a cgroup controller, in case the controller has no children, the initial ref will be dropped in cgroup_kill_sb. In cgroup_rmdir path, the controller is deleted from the parent's children list in css_release_work_fn, which is run on a kernel worker. With this simple script #!/bin/sh mount -t cgroup -o none,name=test test ./tmp mkdir -p ./tmp/abc rmdir ./tmp/abc umount ./tmp sleep 5 cat /proc/self/cgroup The rmdir will remove the last child and umount is expected to kill the parent controller. However, when running the above script, we may get 1:name=test:/ This shows that the parent controller has not been killed. The reason is after rmdir is completed, it is not guaranteed that the parent's children list is empty as css_release_work_fn is deferred to run on a worker. In case cgroup_kill_sb is run before that work, it does not drop the initial ref. Later in the worker, it just removes the child from the list without checking the list is empty to kill the parent controller. As a result, the parent controller still has the initial ref but without any logical refs (children ref, mount ref). This commit adds a free parent controller path into the worker function to free up the parent controller when the last child is killed. Reported-by: kernel test robot Signed-off-by: Bui Quang Minh --- v2: Fix compilation error when CONFIG_CGROUP_BPF is not set kernel/cgroup/cgroup.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) base-commit: 1be9b7206b7dbff54b223eee7ef3bc91b80433aa diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index f01ff231a484..1916070f0d59 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5152,12 +5152,27 @@ static void css_release_work_fn(struct work_struct *work) container_of(work, struct cgroup_subsys_state, destroy_work); struct cgroup_subsys *ss = css->ss; struct cgroup *cgrp = css->cgroup; + struct cgroup *parent = cgroup_parent(cgrp); mutex_lock(&cgroup_mutex); css->flags |= CSS_RELEASED; list_del_rcu(&css->sibling); + /* + * If parent doesn't have any children, start killing it. + * And don't kill the default root. + */ + if (parent && list_empty(&parent->self.children) && + parent != &cgrp_dfl_root.cgrp && + !percpu_ref_is_dying(&parent->self.refcnt)) { +#ifdef CONFIG_CGROUP_BPF + if (!percpu_ref_is_dying(&cgrp->bpf.refcnt)) + cgroup_bpf_offline(parent); +#endif + percpu_ref_kill(&parent->self.refcnt); + } + if (ss) { /* css release path */ if (!list_empty(&css->rstat_css_node)) {