Merge branch 'irq-irqdomain-arm-for-linus' of git://git.kernel.org/pub/scm/linux...

[deliverable/linux.git] / kernel / cgroup.c

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 69f033582a1a2b55a82f33f6dccd283d758df348..bb263d0caab323810f2c30fc3799be467859a7ac 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -277,6 +277,10 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
        if (!(cgrp->root->subsys_mask & (1 << ss->id)))
                return NULL;
 
+       /*
+        * This function is used while updating css associations and thus
+        * can't test the csses directly.  Use ->child_subsys_mask.
+        */
        while (cgroup_parent(cgrp) &&
               !(cgroup_parent(cgrp)->child_subsys_mask & (1 << ss->id)))
                cgrp = cgroup_parent(cgrp);
@@ -284,6 +288,39 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
        return cgroup_css(cgrp, ss);
 }
 
+/**
+ * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest
+ *
+ * Find and get the effective css of @cgrp for @ss.  The effective css is
+ * defined as the matching css of the nearest ancestor including self which
+ * has @ss enabled.  If @ss is not mounted on the hierarchy @cgrp is on,
+ * the root css is returned, so this function always returns a valid css.
+ * The returned css must be put using css_put().
+ */
+struct cgroup_subsys_state *cgroup_get_e_css(struct cgroup *cgrp,
+                                            struct cgroup_subsys *ss)
+{
+       struct cgroup_subsys_state *css;
+
+       rcu_read_lock();
+
+       do {
+               css = cgroup_css(cgrp, ss);
+
+               if (css && css_tryget_online(css))
+                       goto out_unlock;
+               cgrp = cgroup_parent(cgrp);
+       } while (cgrp);
+
+       css = init_css_set.subsys[ss->id];
+       css_get(css);
+out_unlock:
+       rcu_read_unlock();
+       return css;
+}
+
 /* convenient tests for these bits */
 static inline bool cgroup_is_dead(const struct cgroup *cgrp)
 {