netdev - [PATCH v2 4/5] don't take cgroup

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Message-Id: <1335209867-1831-5-git-send-email-glommer@parallels.com>
Date:	Mon, 23 Apr 2012 16:37:46 -0300
From:	Glauber Costa <glommer@...allels.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	<netdev@...r.kernel.org>, <cgroups@...r.kernel.org>,
	Li Zefan <lizefan@...wei.com>,
	<kamezawa.hiroyu@...fujitsu.com>,
	David Miller <davem@...emloft.net>, <devel@...nvz.org>,
	Glauber Costa <glommer@...allels.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: [PATCH v2 4/5] don't take cgroup_mutex in destroy()

Most of the destroy functions are only doing very simple things
like freeing memory.

The ones who goes through lists and such, already use its own
locking for those.

* The cgroup itself won't go away until we free it, (after destroy)
* The parent won't go away because we hold a reference count
* There are no more tasks in the cgroup, and the cgroup is declared
  dead (cgroup_is_removed() == true)

[v2: don't cgroup_lock the freezer and blkcg ]

Signed-off-by: Glauber Costa <glommer@...allels.com>
CC: Tejun Heo <tj@...nel.org>
CC: Li Zefan <lizefan@...wei.com>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC: Vivek Goyal <vgoyal@...hat.com>
---
 kernel/cgroup.c |    9 ++++-----
 1 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 932c318..976d332 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -869,13 +869,13 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 		 * agent */
 		synchronize_rcu();
 
-		mutex_lock(&cgroup_mutex);
 		/*
 		 * Release the subsystem state objects.
 		 */
 		for_each_subsys(cgrp->root, ss)
 			ss->destroy(cgrp);
 
+		mutex_lock(&cgroup_mutex);
 		cgrp->root->number_of_cgroups--;
 		mutex_unlock(&cgroup_mutex);
 
@@ -3994,13 +3994,12 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 
  err_destroy:
 
+	mutex_unlock(&cgroup_mutex);
 	for_each_subsys(root, ss) {
 		if (cgrp->subsys[ss->subsys_id])
 			ss->destroy(cgrp);
 	}
 
-	mutex_unlock(&cgroup_mutex);
-
 	/* Release the reference count that we took on the superblock */
 	deactivate_super(sb);
 
@@ -4349,9 +4348,9 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
 		int ret = cgroup_init_idr(ss, css);
 		if (ret) {
 			dummytop->subsys[ss->subsys_id] = NULL;
+			mutex_unlock(&cgroup_mutex);
 			ss->destroy(dummytop);
 			subsys[i] = NULL;
-			mutex_unlock(&cgroup_mutex);
 			return ret;
 		}
 	}
@@ -4447,10 +4446,10 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
 	 * pointer to find their state. note that this also takes care of
 	 * freeing the css_id.
 	 */
+	mutex_unlock(&cgroup_mutex);
 	ss->destroy(dummytop);
 	dummytop->subsys[ss->subsys_id] = NULL;
 
-	mutex_unlock(&cgroup_mutex);
 }
 EXPORT_SYMBOL_GPL(cgroup_unload_subsys);
 
-- 
1.7.7.6

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