SUNRPC: Fix races with rpc_killall_tasks()

Ensure that we immediately call rpc_exit_task() after waking up, and
that the tk_rpc_status cannot get clobbered by some other function.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/linux/sunrpc/sched.h

@@ -209,6 +209,7 @@ struct rpc_task *rpc_run_task(const struct rpc_task_setup *);
 struct rpc_task *rpc_run_bc_task(struct rpc_rqst *req);
 void		rpc_put_task(struct rpc_task *);
 void		rpc_put_task_async(struct rpc_task *);
+bool		rpc_task_set_rpc_status(struct rpc_task *task, int rpc_status);
 void		rpc_signal_task(struct rpc_task *);
 void		rpc_exit_task(struct rpc_task *);
 void		rpc_exit(struct rpc_task *, int);

net/sunrpc/clnt.c

@@ -1642,7 +1642,7 @@ static void
 __rpc_call_rpcerror(struct rpc_task *task, int tk_status, int rpc_status)
 {
 	trace_rpc_call_rpcerror(task, tk_status, rpc_status);
-	task->tk_rpc_status = rpc_status;
+	rpc_task_set_rpc_status(task, rpc_status);
 	rpc_exit(task, tk_status);
 }
 
@@ -2435,10 +2435,8 @@ rpc_check_timeout(struct rpc_task *task)
 {
 	struct rpc_clnt	*clnt = task->tk_client;
 
-	if (RPC_SIGNALLED(task)) {
-		rpc_call_rpcerror(task, -ERESTARTSYS);
+	if (RPC_SIGNALLED(task))
 		return;
-	}
 
 	if (xprt_adjust_timeout(task->tk_rqstp) == 0)
 		return;

net/sunrpc/sched.c

@@ -65,6 +65,13 @@ gfp_t rpc_task_gfp_mask(void)
 }
 EXPORT_SYMBOL_GPL(rpc_task_gfp_mask);
 
+bool rpc_task_set_rpc_status(struct rpc_task *task, int rpc_status)
+{
+	if (cmpxchg(&task->tk_rpc_status, 0, rpc_status) == 0)
+		return true;
+	return false;
+}
+
 unsigned long
 rpc_task_timeout(const struct rpc_task *task)
 {
@@ -855,12 +862,14 @@ void rpc_signal_task(struct rpc_task *task)
 	if (!RPC_IS_ACTIVATED(task))
 		return;
 
+	if (!rpc_task_set_rpc_status(task, -ERESTARTSYS))
+		return;
 	trace_rpc_task_signalled(task, task->tk_action);
 	set_bit(RPC_TASK_SIGNALLED, &task->tk_runstate);
 	smp_mb__after_atomic();
 	queue = READ_ONCE(task->tk_waitqueue);
 	if (queue)
-		rpc_wake_up_queued_task_set_status(queue, task, -ERESTARTSYS);
+		rpc_wake_up_queued_task(queue, task);
 }
 
 void rpc_exit(struct rpc_task *task, int status)
@@ -907,10 +916,16 @@ static void __rpc_execute(struct rpc_task *task)
 		 * Perform the next FSM step or a pending callback.
 		 *
 		 * tk_action may be NULL if the task has been killed.
-		 * In particular, note that rpc_killall_tasks may
-		 * do this at any time, so beware when dereferencing.
 		 */
 		do_action = task->tk_action;
+		/* Tasks with an RPC error status should exit */
+		if (do_action != rpc_exit_task &&
+		    (status = READ_ONCE(task->tk_rpc_status)) != 0) {
+			task->tk_status = status;
+			if (do_action != NULL)
+				do_action = rpc_exit_task;
+		}
+		/* Callbacks override all actions */
 		if (task->tk_callback) {
 			do_action = task->tk_callback;
 			task->tk_callback = NULL;
@@ -932,14 +947,6 @@ static void __rpc_execute(struct rpc_task *task)
 			continue;
 		}
 
-		/*
-		 * Signalled tasks should exit rather than sleep.
-		 */
-		if (RPC_SIGNALLED(task)) {
-			task->tk_rpc_status = -ERESTARTSYS;
-			rpc_exit(task, -ERESTARTSYS);
-		}
-
 		/*
 		 * The queue->lock protects against races with
 		 * rpc_make_runnable().
@@ -955,6 +962,12 @@ static void __rpc_execute(struct rpc_task *task)
 			spin_unlock(&queue->lock);
 			continue;
 		}
+		/* Wake up any task that has an exit status */
+		if (READ_ONCE(task->tk_rpc_status) != 0) {
+			rpc_wake_up_task_queue_locked(queue, task);
+			spin_unlock(&queue->lock);
+			continue;
+		}
 		rpc_clear_running(task);
 		spin_unlock(&queue->lock);
 		if (task_is_async)
@@ -972,10 +985,7 @@ static void __rpc_execute(struct rpc_task *task)
 			 * clean up after sleeping on some queue, we don't
 			 * break the loop here, but go around once more.
 			 */
-			trace_rpc_task_signalled(task, task->tk_action);
-			set_bit(RPC_TASK_SIGNALLED, &task->tk_runstate);
-			task->tk_rpc_status = -ERESTARTSYS;
-			rpc_exit(task, -ERESTARTSYS);
+			rpc_signal_task(task);
 		}
 		trace_rpc_task_sync_wake(task, task->tk_action);
 	}

net/sunrpc/xprtsock.c

@@ -1978,8 +1978,7 @@ static void xs_local_connect(struct rpc_xprt *xprt, struct rpc_task *task)
 		 * we'll need to figure out how to pass a namespace to
 		 * connect.
 		 */
-		task->tk_rpc_status = -ENOTCONN;
-		rpc_exit(task, -ENOTCONN);
+		rpc_task_set_rpc_status(task, -ENOTCONN);
 		goto out_wake;
 	}
 	ret = xs_local_setup_socket(transport);