[PATCH 1/1] pid_namespace: pidns_get() should check task_active_pid_ns() != NULL

[Oleg Nesterov]

pidns_get()->get_pid_ns() can hit ns == NULL. This task_struct can't
go away, but task_active_pid_ns(task) is NULL if release_task(task)
was already called. Alternatively we could change get_pid_ns(ns) to
check ns != NULL, but it seems that other callers are fine.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

--- x/kernel/pid_namespace.c
+++ x/kernel/pid_namespace.c
@@ -318,7 +318,9 @@ static void *pidns_get(struct task_struct *task)
 	struct pid_namespace *ns;
 
 	rcu_read_lock();
-	ns = get_pid_ns(task_active_pid_ns(task));
+	ns = task_active_pid_ns(task);
+	if (ns)
+		get_pid_ns(ns);
 	rcu_read_unlock();
 
 	return ns;

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