sunrpc: clarify comments on rpc_make_runnable

rpc_make_runnable is not generally called with the queue lock held, unless
it's waking up a task that has been sitting on a waitqueue. This is safe
when the task has not entered the FSM yet, but the comments don't really
spell this out.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/sched.c

@@ -300,8 +300,9 @@ EXPORT_SYMBOL_GPL(__rpc_wait_for_completion_task);
 /*
  * Make an RPC task runnable.
  *
- * Note: If the task is ASYNC, this must be called with
- * the spinlock held to protect the wait queue operation.
+ * Note: If the task is ASYNC, and is being made runnable after sitting on an
+ * rpc_wait_queue, this must be called with the queue spinlock held to protect
+ * the wait queue operation.
  */
 static void rpc_make_runnable(struct rpc_task *task)
 {