From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED2DDC47404 for ; Fri, 4 Oct 2019 10:58:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CF162215EA for ; Fri, 4 Oct 2019 10:58:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729834AbfJDK6G (ORCPT ); Fri, 4 Oct 2019 06:58:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:55138 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725730AbfJDK6F (ORCPT ); Fri, 4 Oct 2019 06:58:05 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id E917EABC6; Fri, 4 Oct 2019 10:58:02 +0000 (UTC) From: =?UTF-8?q?Michal=20Koutn=C3=BD?= To: cgroups@vger.kernel.org Cc: Tejun Heo , linux-kernel@vger.kernel.org, Li Zefan , Johannes Weiner Subject: [PATCH 1/5] cgroup: Update comments about task exit path Date: Fri, 4 Oct 2019 12:57:39 +0200 Message-Id: <20191004105743.363-2-mkoutny@suse.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20191004105743.363-1-mkoutny@suse.com> References: <20191004105743.363-1-mkoutny@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We no longer take cgroup_mutex in cgroup_exit and the exiting tasks are not moved to init_css_set, reflect that in several comments to prevent confusion. Signed-off-by: Michal Koutný --- kernel/cgroup/cgroup.c | 29 +++++++++-------------------- 1 file changed, 9 insertions(+), 20 deletions(-) diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 753afbca549f..1488bb732902 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -899,8 +899,7 @@ static void css_set_move_task(struct task_struct *task, /* * We are synchronized through cgroup_threadgroup_rwsem * against PF_EXITING setting such that we can't race - * against cgroup_exit() changing the css_set to - * init_css_set and dropping the old one. + * against cgroup_exit()/cgroup_free() dropping the css_set. */ WARN_ON_ONCE(task->flags & PF_EXITING); @@ -1430,9 +1429,8 @@ struct cgroup *task_cgroup_from_root(struct task_struct *task, struct cgroup_root *root) { /* - * No need to lock the task - since we hold cgroup_mutex the - * task can't change groups, so the only thing that can happen - * is that it exits and its css is set back to init_css_set. + * No need to lock the task - since we hold css_set_lock the + * task can't change groups. */ return cset_cgroup_from_root(task_css_set(task), root); } @@ -6020,7 +6018,7 @@ void cgroup_post_fork(struct task_struct *child) struct css_set *cset; spin_lock_irq(&css_set_lock); - cset = task_css_set(current); + cset = task_css_set(current); /* current is @child's parent */ if (list_empty(&child->cg_list)) { get_css_set(cset); cset->nr_tasks++; @@ -6063,20 +6061,8 @@ void cgroup_post_fork(struct task_struct *child) * cgroup_exit - detach cgroup from exiting task * @tsk: pointer to task_struct of exiting process * - * Description: Detach cgroup from @tsk and release it. - * - * Note that cgroups marked notify_on_release force every task in - * them to take the global cgroup_mutex mutex when exiting. - * This could impact scaling on very large systems. Be reluctant to - * use notify_on_release cgroups where very high task exit scaling - * is required on large systems. + * Description: Detach cgroup from @tsk. * - * We set the exiting tasks cgroup to the root cgroup (top_cgroup). We - * call cgroup_exit() while the task is still competent to handle - * notify_on_release(), then leave the task attached to the root cgroup in - * each hierarchy for the remainder of its exit. No need to bother with - * init_css_set refcnting. init_css_set never goes away and we can't race - * with migration path - PF_EXITING is visible to migration path. */ void cgroup_exit(struct task_struct *tsk) { @@ -6086,7 +6072,8 @@ void cgroup_exit(struct task_struct *tsk) /* * Unlink from @tsk from its css_set. As migration path can't race - * with us, we can check css_set and cg_list without synchronization. + * with us (thanks to cgroup_threadgroup_rwsem), we can check css_set + * and cg_list without synchronization. */ cset = task_css_set(tsk); @@ -6102,6 +6089,8 @@ void cgroup_exit(struct task_struct *tsk) spin_unlock_irq(&css_set_lock); } else { + /* Take reference to avoid freeing init_css_set in cgroup_free, + * see cgroup_fork(). */ get_css_set(cset); } -- 2.21.0