From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH 07/11] cgroup: drop unnecessary RCU dancing from __put_css_set() Date: Wed, 12 Jun 2013 21:04:54 -0700 Message-ID: <1371096298-24402-8-git-send-email-tj@kernel.org> References: <1371096298-24402-1-git-send-email-tj@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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:x-mailer:in-reply-to :references; bh=fW9gw/dTOkqi/FvfbJM1YM836AZjHpT8FxrZCh8ebnI=; b=jmbmRdXxztK/JyD5QueLZ6c6XZq9J7MmkkcdDpjEf/+/MvsCegAJP/+2qKfFZhWRWg BObbfsedky165kgt0i767DYOjoIcKYOKtqNnj+OD4HdZtIhEVK+6NOPTbFQKO9exXIeP mVEBQtq3eiG2tseNXwLY87JwnJknBIweiJtLRqKHnwGv57VGO+3KMq4KqMvdWc29z5n0 jBRaJFuyYPm9dgPeE1vQ9CSolvJC0ZMMHmJLwYRCe/p0rOfICqkjB5cGSQF2AtDnto4u u6RdakpLLL9WWx0r1ZWBz5ceznVqoWSS50Z2769JLItO818iTVq8AoW904RhggRXk5mk MJSQ== In-Reply-To: <1371096298-24402-1-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org Cc: cl-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Tejun Heo , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, koverstreet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org __put_css_set() does RCU read access on @cgrp across dropping @cgrp->count so that it can continue accessing @cgrp even if the count reached zero and destruction of the cgroup commenced. Given that both sides - __css_put() and cgroup_destroy_locked() - are cold paths, this is unnecessary. Just making cgroup_destroy_locked() grab css_set_lock while checking @cgrp->count is enough. Remove the RCU read locking from __put_css_set() and make cgroup_destroy_locked() read-lock css_set_lock when checking @cgrp->count. This will also allow removing @cgrp->count. Signed-off-by: Tejun Heo --- kernel/cgroup.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 8f5fbcb..22f9729 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -407,19 +407,13 @@ static void __put_css_set(struct css_set *cset, int taskexit) list_del(&link->cset_link); list_del(&link->cgrp_link); - /* - * We may not be holding cgroup_mutex, and if cgrp->count is - * dropped to 0 the cgroup can be destroyed at any time, hence - * rcu_read_lock is used to keep it alive. - */ - rcu_read_lock(); + /* @cgrp can't go away while we're holding css_set_lock */ if (atomic_dec_and_test(&cgrp->count) && notify_on_release(cgrp)) { if (taskexit) set_bit(CGRP_RELEASABLE, &cgrp->flags); check_for_release(cgrp); } - rcu_read_unlock(); kfree(link); } @@ -4373,11 +4367,19 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) struct cgroup *parent = cgrp->parent; struct cgroup_event *event, *tmp; struct cgroup_subsys *ss; + bool empty; lockdep_assert_held(&d->d_inode->i_mutex); lockdep_assert_held(&cgroup_mutex); - if (atomic_read(&cgrp->count) || !list_empty(&cgrp->children)) + /* + * css_set_lock prevents @cgrp from being removed while + * __put_css_set() is in progress. + */ + read_lock(&css_set_lock); + empty = !atomic_read(&cgrp->count) && list_empty(&cgrp->children); + read_unlock(&css_set_lock); + if (!empty) return -EBUSY; /* @@ -5054,8 +5056,6 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks) static void check_for_release(struct cgroup *cgrp) { - /* All of these checks rely on RCU to keep the cgroup - * structure alive */ if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count) && list_empty(&cgrp->children)) { /* -- 1.8.2.1