[PATCH cgroup/for-3.11] cgroup: grab cgroup_mutex indrop_parsed_module_refcounts()

[Tejun Heo]

This isn't strictly necessary as all subsystems specified in
@subsys_mask are guaranteed to be pinned; however, it does spuriously
trigger lockdep warning.  Let's grab cgroup_mutex around it.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 kernel/cgroup.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1325,11 +1325,11 @@ static void drop_parsed_module_refcounts
 	struct cgroup_subsys *ss;
 	int i;
 
-	for_each_subsys(ss, i) {
-		if (!(subsys_mask & (1UL << i)))
-			continue;
-		module_put(cgroup_subsys[i]->module);
-	}
+	mutex_lock(&cgroup_mutex);
+	for_each_subsys(ss, i)
+		if (subsys_mask & (1UL << i))
+			module_put(cgroup_subsys[i]->module);
+	mutex_unlock(&cgroup_mutex);
 }
 
 static int cgroup_remount(struct super_block *sb, int *flags, char *data)
--
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