3 files changed, 31 insertions, 21 deletions

diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 09f4c7df1478..ae7bc1e70085 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -263,11 +263,16 @@ struct cgroup {
 
         /*
          * Each non-empty css_set associated with this cgroup contributes
-         * one to populated_cnt.  All children with non-zero popuplated_cnt
-         * of their own contribute one.  The count is zero iff there's no
-         * task in this cgroup or its subtree.
+         * one to nr_populated_csets.  The counter is zero iff this cgroup
+         * doesn't have any tasks.
+         *
+         * All children which have non-zero nr_populated_csets and/or
+         * nr_populated_children of their own contribute one to
+         * nr_populated_children.  The counter is zero iff this cgroup's
+         * subtree proper doesn't have any tasks.
          */
-        int populated_cnt;
+        int nr_populated_csets;
+        int nr_populated_children;
 
         struct kernfs_node *kn;         /* cgroup kernfs entry */
         struct cgroup_file procs_file;  /* handle for "cgroup.procs" */
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 710a005c6b7a..308b10797a54 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -537,7 +537,7 @@ static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 /* no synchronization, the result can only be used as a hint */
 static inline bool cgroup_is_populated(struct cgroup *cgrp)
 {
-        return cgrp->populated_cnt;
+        return cgrp->nr_populated_csets + cgrp->nr_populated_children;
 }
 
 /* returns ino associated with a cgroup */
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 4f02b5edd82c..5fe2644cd0f3 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -587,39 +587,44 @@ static bool css_set_populated(struct css_set *cset)
 }
 
 /**
- * cgroup_update_populated - updated populated count of a cgroup
+ * cgroup_update_populated - update the populated count of a cgroup
  * @cgrp: the target cgroup
  * @populated: inc or dec populated count
  *
  * One of the css_sets associated with @cgrp is either getting its first
- * task or losing the last.  Update @cgrp->populated_cnt accordingly.  The
- * count is propagated towards root so that a given cgroup's populated_cnt
- * is zero iff the cgroup and all its descendants don't contain any tasks.
+ * task or losing the last.  Update @cgrp->nr_populated_* accordingly.  The
+ * count is propagated towards root so that a given cgroup's
+ * nr_populated_children is zero iff none of its descendants contain any
+ * tasks.
  *
- * @cgrp's interface file "cgroup.populated" is zero if
- * @cgrp->populated_cnt is zero and 1 otherwise.  When @cgrp->populated_cnt
- * changes from or to zero, userland is notified that the content of the
- * interface file has changed.  This can be used to detect when @cgrp and
- * its descendants become populated or empty.
+ * @cgrp's interface file "cgroup.populated" is zero if both
+ * @cgrp->nr_populated_csets and @cgrp->nr_populated_children are zero and
+ * 1 otherwise.  When the sum changes from or to zero, userland is notified
+ * that the content of the interface file has changed.  This can be used to
+ * detect when @cgrp and its descendants become populated or empty.
  */
 static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
 {
+        struct cgroup *child = NULL;
+        int adj = populated ? 1 : -1;
+
         lockdep_assert_held(&css_set_lock);
 
         do {
-                bool trigger;
+                bool was_populated = cgroup_is_populated(cgrp);
 
-                if (populated)
-                        trigger = !cgrp->populated_cnt++;
+                if (!child)
+                        cgrp->nr_populated_csets += adj;
                 else
-                        trigger = !--cgrp->populated_cnt;
+                        cgrp->nr_populated_children += adj;
 
-                if (!trigger)
+                if (was_populated == cgroup_is_populated(cgrp))
                         break;
 
                 cgroup1_check_for_release(cgrp);
                 cgroup_file_notify(&cgrp->events_file);
 
+                child = cgrp;
                 cgrp = cgroup_parent(cgrp);
         } while (cgrp);
 }
@@ -630,7 +635,7 @@ static void cgroup_update_populated(struct cgroup *cgrp, bool populated)
  * @populated: whether @cset is populated or depopulated
  *
  * @cset is either getting the first task or losing the last.  Update the
- * ->populated_cnt of all associated cgroups accordingly.
+ * populated counters of all associated cgroups accordingly.
  */
 static void css_set_update_populated(struct css_set *cset, bool populated)
 {
@@ -653,7 +658,7 @@ static void css_set_update_populated(struct css_set *cset, bool populated)
  * css_set, @from_cset can be NULL.  If @task is being disassociated
  * instead of moved, @to_cset can be NULL.
  *
- * This function automatically handles populated_cnt updates and
+ * This function automatically handles populated counter updates and
  * css_task_iter adjustments but the caller is responsible for managing
  * @from_cset and @to_cset's reference counts.
  */