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-rw-r--r--include/linux/cgroup.h10
1 files changed, 8 insertions, 2 deletions
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 7620a8bc0493..8be03520995c 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -462,7 +462,7 @@ 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)
@@ -472,7 +472,13 @@ 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();
}