From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frederic Weisbecker Subject: [PATCH 1/2] cgroup: Remove unnecessary task_lock before fetching css_set on migration Date: Tue, 20 Dec 2011 20:01:12 +0100 Message-ID: <1324407673-18975-1-git-send-email-fweisbec@gmail.com> References: <1324320274-18485-1-git-send-email-msb@chromium.org> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=from:to:cc:subject:date:message-id:x-mailer:in-reply-to:references; bh=q6+wITvHhIQHbNsBRkOR5mKzg2/olBhmzgDTAb/n1Fk=; b=SctSXJysvqDsEGiZfm1uaMUd3HSZ+78HIA4fo0ustRMHkAldGOX+rSjB4f57EnLQgn eh/FzU6eUrL0KsbVEETRBev0dGEbW35eU1GyzhX64YbzdvkZ7LpE0fnByncg5O/GMN20 MFC4I5FsCZxg6HnrOngzwM3yJems/xLjk/k8k= In-Reply-To: <1324320274-18485-1-git-send-email-msb-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tejun Heo , Li Zefan Cc: LKML , Frederic Weisbecker , Containers , Cgroups , KAMEZAWA Hiroyuki , Oleg Nesterov , Andrew Morton , Paul Menage , Mandeep Singh Baines When we fetch the css_set of the tasks on cgroup migration, we don't need anymore to synchronize against cgroup_exit() that could swap the old one with init_css_set. Now that we are using threadgroup_lock() during the migrations, we don't need to worry about it anymore. Signed-off-by: Frederic Weisbecker Cc: Tejun Heo Cc: Li Zefan Cc: Containers Cc: Cgroups Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage Cc: Mandeep Singh Baines --- kernel/cgroup.c | 21 +++++++++++---------- 1 files changed, 11 insertions(+), 10 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 5fdd98c..6b5f693 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1850,13 +1850,13 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, struct css_set *newcg; /* - * get old css_set. we need to take task_lock and refcount it, because - * an exiting task can change its css_set to init_css_set and drop its - * old one without taking cgroup_mutex. + * 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. */ - task_lock(tsk); + WARN_ON_ONCE(tsk->flags & PF_EXITING); oldcg = tsk->cgroups; - task_unlock(tsk); /* locate or allocate a new css_set for this task. */ if (guarantee) { @@ -1875,9 +1875,7 @@ static int cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp, return -ENOMEM; } - /* @tsk can't exit as its threadgroup is locked */ task_lock(tsk); - WARN_ON_ONCE(tsk->flags & PF_EXITING); rcu_assign_pointer(tsk->cgroups, newcg); task_unlock(tsk); @@ -2177,10 +2175,13 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) /* nothing to do if this task is already in the cgroup */ if (tc->cgrp == cgrp) continue; - /* get old css_set pointer */ - task_lock(tc->task); + /* + * get old css_set pointer. threadgroup is locked so this is + * safe against concurrent cgroup_exit() changing this to + * init_css_set. + */ oldcg = tc->task->cgroups; - task_unlock(tc->task); + /* if we don't already have it in the list get a new one */ if (!css_set_fetched(cgrp, tc->task, oldcg, &newcg_list)) if (css_set_prefetch(cgrp, oldcg, &newcg_list)) -- 1.7.5.4