1 files changed, 55 insertions, 18 deletions

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index aae10baf1902..4c1cf0969a80 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -492,7 +492,7 @@ static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
 }
 
 /**
- * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
+ * cgroup_e_css_by_mask - obtain a cgroup's effective css for the specified ss
  * @cgrp: the cgroup of interest
  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
  *
@@ -501,8 +501,8 @@ static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
  * enabled.  If @ss is associated with the hierarchy @cgrp is on, this
  * function is guaranteed to return non-NULL css.
  */
-static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
-						struct cgroup_subsys *ss)
+static struct cgroup_subsys_state *cgroup_e_css_by_mask(struct cgroup *cgrp,
+							struct cgroup_subsys *ss)
 {
 	lockdep_assert_held(&cgroup_mutex);
 
@@ -523,6 +523,35 @@ static struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
 }
 
 /**
+ * cgroup_e_css - obtain 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 is not guaranteed to be online, and therefore it is the
+ * callers responsiblity to tryget a reference for it.
+ */
+struct cgroup_subsys_state *cgroup_e_css(struct cgroup *cgrp,
+					 struct cgroup_subsys *ss)
+{
+	struct cgroup_subsys_state *css;
+
+	do {
+		css = cgroup_css(cgrp, ss);
+
+		if (css)
+			return css;
+		cgrp = cgroup_parent(cgrp);
+	} while (cgrp);
+
+	return init_css_set.subsys[ss->id];
+}
+
+/**
  * cgroup_get_e_css - get a cgroup's effective css for the specified subsystem
  * @cgrp: the cgroup of interest
  * @ss: the subsystem of interest
@@ -604,10 +633,11 @@ EXPORT_SYMBOL_GPL(of_css);
  *
  * Should be called under cgroup_[tree_]mutex.
  */
-#define for_each_e_css(css, ssid, cgrp)					\
-	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	\
-		if (!((css) = cgroup_e_css(cgrp, cgroup_subsys[(ssid)]))) \
-			;						\
+#define for_each_e_css(css, ssid, cgrp)					    \
+	for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++)	    \
+		if (!((css) = cgroup_e_css_by_mask(cgrp,		    \
+						   cgroup_subsys[(ssid)]))) \
+			;						    \
 		else
 
 /**
@@ -1006,7 +1036,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset,
 			 * @ss is in this hierarchy, so we want the
 			 * effective css from @cgrp.
 			 */
-			template[i] = cgroup_e_css(cgrp, ss);
+			template[i] = cgroup_e_css_by_mask(cgrp, ss);
 		} else {
 			/*
 			 * @ss is not in this hierarchy, so we don't want
@@ -2836,11 +2866,12 @@ restart:
 }
 
 /**
- * cgroup_save_control - save control masks of a subtree
+ * cgroup_save_control - save control masks and dom_cgrp of a subtree
  * @cgrp: root of the target subtree
  *
- * Save ->subtree_control and ->subtree_ss_mask to the respective old_
- * prefixed fields for @cgrp's subtree including @cgrp itself.
+ * Save ->subtree_control, ->subtree_ss_mask and ->dom_cgrp to the
+ * respective old_ prefixed fields for @cgrp's subtree including @cgrp
+ * itself.
  */
 static void cgroup_save_control(struct cgroup *cgrp)
 {
@@ -2850,6 +2881,7 @@ static void cgroup_save_control(struct cgroup *cgrp)
 	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {
 		dsct->old_subtree_control = dsct->subtree_control;
 		dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;
+		dsct->old_dom_cgrp = dsct->dom_cgrp;
 	}
 }
 
@@ -2875,11 +2907,12 @@ static void cgroup_propagate_control(struct cgroup *cgrp)
 }
 
 /**
- * cgroup_restore_control - restore control masks of a subtree
+ * cgroup_restore_control - restore control masks and dom_cgrp of a subtree
  * @cgrp: root of the target subtree
  *
- * Restore ->subtree_control and ->subtree_ss_mask from the respective old_
- * prefixed fields for @cgrp's subtree including @cgrp itself.
+ * Restore ->subtree_control, ->subtree_ss_mask and ->dom_cgrp from the
+ * respective old_ prefixed fields for @cgrp's subtree including @cgrp
+ * itself.
  */
 static void cgroup_restore_control(struct cgroup *cgrp)
 {
@@ -2889,6 +2922,7 @@ static void cgroup_restore_control(struct cgroup *cgrp)
 	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {
 		dsct->subtree_control = dsct->old_subtree_control;
 		dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;
+		dsct->dom_cgrp = dsct->old_dom_cgrp;
 	}
 }
 
@@ -3019,7 +3053,7 @@ static int cgroup_apply_control(struct cgroup *cgrp)
 		return ret;
 
 	/*
-	 * At this point, cgroup_e_css() results reflect the new csses
+	 * At this point, cgroup_e_css_by_mask() results reflect the new csses
 	 * making the following cgroup_update_dfl_csses() properly update
 	 * css associations of all tasks in the subtree.
 	 */
@@ -3196,6 +3230,8 @@ static int cgroup_enable_threaded(struct cgroup *cgrp)
 {
 	struct cgroup *parent = cgroup_parent(cgrp);
 	struct cgroup *dom_cgrp = parent->dom_cgrp;
+	struct cgroup *dsct;
+	struct cgroup_subsys_state *d_css;
 	int ret;
 
 	lockdep_assert_held(&cgroup_mutex);
@@ -3225,12 +3261,13 @@ static int cgroup_enable_threaded(struct cgroup *cgrp)
 	 */
 	cgroup_save_control(cgrp);
 
-	cgrp->dom_cgrp = dom_cgrp;
+	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)
+		if (dsct == cgrp || cgroup_is_threaded(dsct))
+			dsct->dom_cgrp = dom_cgrp;
+
 	ret = cgroup_apply_control(cgrp);
 	if (!ret)
 		parent->nr_threaded_children++;
-	else
-		cgrp->dom_cgrp = cgrp;
 
 	cgroup_finalize_control(cgrp, ret);
 	return ret;