Merge tag 'v4.19.59-rt24' into toradex_4.19.y-rttoradex_4.19.y-rt

Linux 4.19.59-rt24

1 files changed, 8 insertions, 2 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ca51b2c15bcc..8937d48a5389 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -485,7 +485,7 @@ static inline struct cgroup_subsys_state *task_css(struct task_struct *task,
  *
  * Find the css for the (@task, @subsys_id) combination, increment a
  * reference on and return it.  This function is guaranteed to return a
- * valid css.
+ * valid css.  The returned css may already have been offlined.
  */
 static inline struct cgroup_subsys_state *
 task_get_css(struct task_struct *task, int subsys_id)
@@ -495,7 +495,13 @@ task_get_css(struct task_struct *task, int subsys_id)
 	rcu_read_lock();
 	while (true) {
 		css = task_css(task, subsys_id);
-		if (likely(css_tryget_online(css)))
+		/*
+		 * Can't use css_tryget_online() here.  A task which has
+		 * PF_EXITING set may stay associated with an offline css.
+		 * If such task calls this function, css_tryget_online()
+		 * will keep failing.
+		 */
+		if (likely(css_tryget(css)))
 			break;
 		cpu_relax();
 	}