cgroup: hold cgroup_mutex before calling css_offline()

cpuset no longer nests cgroup_mutex inside cpu_hotplug lock, so
we don't have to release cgroup_mutex before calling css_offline().

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

2 files changed, 2 insertions, 10 deletions

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index bcf1a00b06a1..0028e888828c 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -580,6 +580,7 @@ propagation along the hierarchy. See the comment on
 cgroup_for_each_descendant_pre() for details.
 
 void css_offline(struct cgroup *cgrp);
+(cgroup_mutex held by caller)
 
 This is the counterpart of css_online() and called iff css_online()
 has succeeded on @cgrp. This signifies the beginning of the end of
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index fd0b056d8da5..49297cbc134d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4169,17 +4169,8 @@ static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
         if (!(css->flags & CSS_ONLINE))
                 return;
 
-        /*
-         * css_offline() should be called with cgroup_mutex unlocked.  See
-         * 3fa59dfbc3 ("cgroup: fix potential deadlock in pre_destroy") for
-         * details.  This temporary unlocking should go away once
-         * cgroup_mutex is unexported from controllers.
-         */
-        if (ss->css_offline) {
-                mutex_unlock(&cgroup_mutex);
+        if (ss->css_offline)
                 ss->css_offline(cgrp);
-                mutex_lock(&cgroup_mutex);
-        }
 
         cgrp->subsys[ss->subsys_id]->flags &= ~CSS_ONLINE;
 }