linux-kernel - [PATCH] cgroups: remove rcu_read_lock() in cgroupstats

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Message-ID: <49278602.2000707@cn.fujitsu.com>
Date:	Sat, 22 Nov 2008 12:09:38 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] cgroups: remove rcu_read_lock() in cgroupstats_build()


cgroup_iter_* do not need rcu_read_lock().

In cgroup_enable_task_cg_lists(), do_each_thread() and
while_each_thread() are protected by RCU,
it's OK, for write_lock(&css_set_lock) implies rcu_read_lock() in non-RT kernel.

If we need explicit rcu_read_lock(), we should add rcu_read_lock()
in cgroup_enable_task_cg_lists(), not cgroup_iter_*.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 358e775..e6d92a5 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2047,7 +2047,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 
 	ret = 0;
 	cgrp = dentry->d_fsdata;
-	rcu_read_lock();
 
 	cgroup_iter_start(cgrp, &it);
 	while ((tsk = cgroup_iter_next(cgrp, &it))) {
@@ -2072,7 +2071,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 	}
 	cgroup_iter_end(cgrp, &it);
 
-	rcu_read_unlock();
 err:
 	return ret;
 }


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