From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH 03/14] cgroup: add cgroup_subsys_state->parent Date: Thu, 8 Aug 2013 16:13:40 -0400 Message-ID: <1375992831-4650-4-git-send-email-tj@kernel.org> References: <1375992831-4650-1-git-send-email-tj@kernel.org> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=5kX1P3wg02LmP5QQuBwQqQPc4D1s9TrihYvdBkI9JEs=; b=LiXydF7ZXXpjYi5DtV7RCTLo3kPjU3qOecJrkBAKhSI3lE+bt7IZ2fbNAEcfk8uYk5 lL6kfJdOcEY/0BguH+ude8ojIrj9sr507EhWGmfDmDGftqeel541ALaw6fzCXDw75c0R rx98CXOh5Xf3zx0ULXKd3WclkDwMEPNrMbMqbsvUWzcriyYK5634Ie9rGWWoYoLND+LZ l/5/laCOWxCBSUDyvnlIeoHZp+Vhs4hAB6lBbGcMssdbwkeWtgtLBDJl3qd1J7A+C0ru OncyzqDnsRm7BXdCubs3jMAlwES4tCcW5vwbDSQuPXaABL+srLNtRriWJjBgbJEkgkcL +STQ== In-Reply-To: <1375992831-4650-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lizefan@huawei.com Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Tejun Heo With the planned unified hierarchy, css's (cgroup_subsys_state) will be RCU protected and allowed to be attached and detached dynamically over the course of a cgroup's lifetime. This means that css's will stay accessible after being detached from its cgroup - the matching pointer in cgroup->subsys[] cleared - for ref draining and RCU grace period. cgroup core still wants to guarantee that the parent css is never destroyed before its children and css_parent() always returns the parent regardless of the state of the child css as long as it's accessible. This patch makes css's hold onto their parents and adds css->parent so that the parent css is never detroyed before its children and can be determined without consulting the cgroups. cgroup->dummy_css is also updated to point to the parent dummy_css; however, it doesn't need to worry about object lifetime as the parent cgroup is already pinned by the child. Signed-off-by: Tejun Heo --- include/linux/cgroup.h | 13 ++++--------- kernel/cgroup.c | 18 +++++++++++++++--- 2 files changed, 19 insertions(+), 12 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 12d66fe..8a5dc91 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -75,6 +75,9 @@ struct cgroup_subsys_state { /* reference count - access via css_[try]get() and css_put() */ struct percpu_ref refcnt; + /* the parent css */ + struct cgroup_subsys_state *parent; + unsigned long flags; /* ID for this css, if possible */ struct css_id __rcu *id; @@ -666,15 +669,7 @@ struct cgroup_subsys { static inline struct cgroup_subsys_state *css_parent(struct cgroup_subsys_state *css) { - struct cgroup *parent_cgrp = css->cgroup->parent; - - if (!parent_cgrp) - return NULL; - - if (css->ss) - return parent_cgrp->subsys[css->ss->subsys_id]; - else - return &parent_cgrp->dummy_css; + return css->parent; } /** diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 0b28097..5c6dd7e 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4264,6 +4264,9 @@ static void css_free_work_fn(struct work_struct *work) struct cgroup_subsys_state *css = container_of(work, struct cgroup_subsys_state, destroy_work); + if (css->parent) + css_put(css->parent); + cgroup_dput(css->cgroup); } @@ -4290,8 +4293,12 @@ static void init_cgroup_css(struct cgroup_subsys_state *css, css->ss = ss; css->flags = 0; css->id = NULL; - if (cgrp == cgroup_dummy_top) + + if (cgrp->parent) + css->parent = cgroup_css(cgrp->parent, ss->subsys_id); + else css->flags |= CSS_ROOT; + BUG_ON(cgroup_css(cgrp, ss->subsys_id)); cgrp->subsys[ss->subsys_id] = css; } @@ -4388,6 +4395,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, cgrp->dentry = dentry; cgrp->parent = parent; + cgrp->dummy_css.parent = &parent->dummy_css; cgrp->root = parent->root; if (notify_on_release(parent)) @@ -4436,9 +4444,13 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children); root->number_of_cgroups++; - /* each css holds a ref to the cgroup's dentry */ - for_each_root_subsys(root, ss) + /* each css holds a ref to the cgroup's dentry and the parent css */ + for_each_root_subsys(root, ss) { + struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); + dget(dentry); + percpu_ref_get(&css->parent->refcnt); + } /* hold a ref to the parent's dentry */ dget(parent->dentry); -- 1.8.3.1