linux-kernel - [PATCH v2 4/6] cgroup: remove duplicate RCU free on struct cgroup

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Date:	Thu, 24 Jan 2013 14:31:27 +0800
From:	Li Zefan <lizefan@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: [PATCH v2 4/6] cgroup: remove duplicate RCU free on struct cgroup

When destroying a cgroup, though in cgroup_diput() we've called
synchronize_rcu(), we then still have to free it via call_rcu().

The story is, long ago to fix a race between reading /proc/sched_debug
and freeing cgroup, the code was changed to utilize call_rcu(). See
commit a47295e6bc42ad35f9c15ac66f598aa24debd4e2 ("cgroups: make
cgroup_path() RCU-safe")

As we've fixed cpu cgroup that cpu_cgroup_offline_css() is used
to unregister a task_group so there won't be concurrent access
to this task_group after synchronize_rcu() in diput(). Now we can
just kfree(cgrp).

Signed-off-by: Li Zefan <lizefan@...wei.com>
---
 kernel/cgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b9a76e2..a39e2b0 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -892,7 +892,7 @@ static void cgroup_diput(struct dentry *dentry, struct inode *inode)
 		simple_xattrs_free(&cgrp->xattrs);

 		ida_simple_remove(&cgrp->root->cgroup_ida, cgrp->id);
-		kfree_rcu(cgrp, rcu_head);
+		kfree(cgrp);
 	} else {
 		struct cfent *cfe = __d_cfe(dentry);
 		struct cgroup *cgrp = dentry->d_parent->d_fsdata;
-- 
1.8.0.2
--
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