From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754845Ab1LVETd (ORCPT ); Wed, 21 Dec 2011 23:19:33 -0500 Received: from mail-ee0-f74.google.com ([74.125.83.74]:34980 "EHLO mail-ee0-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754653Ab1LVESu (ORCPT ); Wed, 21 Dec 2011 23:18:50 -0500 From: Mandeep Singh Baines To: Tejun Heo , Li Zefan , Frederic Weisbecker , linux-kernel@vger.kernel.org Cc: Mandeep Singh Baines , Tejun Heo , Li Zefan , containers@lists.linux-foundation.org, cgroups@vger.kernel.org, KAMEZAWA Hiroyuki , Frederic Weisbecker , Oleg Nesterov , Andrew Morton , Paul Menage Subject: [PATCH 1/4] cgroup: remove redundant get/put of old css_set from migrate Date: Wed, 21 Dec 2011 20:18:35 -0800 Message-Id: <1324527518-24461-1-git-send-email-msb@chromium.org> X-Mailer: git-send-email 1.7.3.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We can now assume that the css_set reference held by the task will not go away for an exiting task. PF_EXITING state can be trusted throughout migration by checking it after locking threadgroup. While at it, renamed css_set_check_fetched to css_set_fetched. !css_set_fetched() seems to read better than !css_set_check_fetched(). Changes in V4: * https://lkml.org/lkml/2011/12/20/368 (Tejun Heo) * Fix typo in commit message * Undid the rename of css_set_check_fetched * https://lkml.org/lkml/2011/12/20/427 (Li Zefan) * Fix comment in cgroup_task_migrate() Changes in V3: * https://lkml.org/lkml/2011/12/20/255 (Frederic Weisbecker) * Fixed to put error in retval Changes in V2: * https://lkml.org/lkml/2011/12/19/289 (Tejun Heo) * Updated commit message Signed-off-by: Mandeep Singh Baines Cc: Tejun Heo Cc: Li Zefan Cc: containers@lists.linux-foundation.org Cc: cgroups@vger.kernel.org Cc: KAMEZAWA Hiroyuki Cc: Frederic Weisbecker Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage --- kernel/cgroup.c | 28 ++++++++-------------------- 1 files changed, 8 insertions(+), 20 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 4936d88..8228808 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1850,14 +1850,12 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, struct css_set *newcg; /* - * get old css_set. We are synchronized through threadgroup_lock() - * 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. + * We are synchronized through threadgroup_lock() 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. */ WARN_ON_ONCE(tsk->flags & PF_EXITING); oldcg = tsk->cgroups; - get_css_set(oldcg); /* locate or allocate a new css_set for this task. */ if (guarantee) { @@ -1872,12 +1870,9 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, might_sleep(); /* find_css_set will give us newcg already referenced. */ newcg = find_css_set(oldcg, cgrp); - if (!newcg) { - put_css_set(oldcg); + if (!newcg) return -ENOMEM; - } } - put_css_set(oldcg); task_lock(tsk); rcu_assign_pointer(tsk->cgroups, newcg); @@ -2186,18 +2181,11 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) * init_css_set. */ oldcg = tc->task->cgroups; - get_css_set(oldcg); - /* see if the new one for us is already in the list? */ - if (css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list)) { - /* was already there, nothing to do. */ - put_css_set(oldcg); - } else { - /* we don't already have it. get new one. */ - retval = css_set_prefetch(cgrp, oldcg, &newcg_list); - put_css_set(oldcg); - if (retval) + + /* if we don't already have it in the list get a new one */ + if (!css_set_check_fetched(cgrp, tc->task, oldcg, &newcg_list)) + if (retval = css_set_prefetch(cgrp, oldcg, &newcg_list)) goto out_list_teardown; - } } /* -- 1.7.3.1