1 files changed, 17 insertions, 0 deletions
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index f4f8cb0435b4..fc21c5d5fd5d 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -244,7 +244,24 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 		set_current_state(TASK_INTERRUPTIBLE);
 		if (pid_ns->pid_allocated == init_pids)
 			break;
+		/*
+		 * Release tasks_rcu_exit_srcu to avoid following deadlock:
+		 *
+		 * 1) TASK A unshare(CLONE_NEWPID)
+		 * 2) TASK A fork() twice -> TASK B (child reaper for new ns)
+		 *    and TASK C
+		 * 3) TASK B exits, kills TASK C, waits for TASK A to reap it
+		 * 4) TASK A calls synchronize_rcu_tasks()
+		 *                   -> synchronize_srcu(tasks_rcu_exit_srcu)
+		 * 5) *DEADLOCK*
+		 *
+		 * It is considered safe to release tasks_rcu_exit_srcu here
+		 * because we assume the current task can not be concurrently
+		 * reaped at this point.
+		 */
+		exit_tasks_rcu_stop();
 		schedule();
+		exit_tasks_rcu_start();
 	}
 	__set_current_state(TASK_RUNNING);