SUNRPC: Prevent looping due to rpc_signal_task() races

If rpc_signal_task() is called while a task is in an rpc_call_done()
callback function, and the latter calls rpc_restart_call(), the task can
end up looping due to the RPC_TASK_SIGNALLED flag being set without the
tk_rpc_status being set.
Removing the redundant mechanism for signalling the task fixes the
looping behaviour.

Reported-by: Li Lingfeng <[email protected]>
Fixes: 3949419 ("SUNRPC: Fix races with rpc_killall_tasks()")
Signed-off-by: Trond Myklebust <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Anna Schumaker <[email protected]>

Author: Trond Myklebust

include/linux/sunrpc/sched.h

@@ -158,7 +158,6 @@ enum {
 	RPC_TASK_NEED_XMIT,
 	RPC_TASK_NEED_RECV,
 	RPC_TASK_MSG_PIN_WAIT,
-	RPC_TASK_SIGNALLED,
 };
 
 #define rpc_test_and_set_running(t) \
@@ -171,7 +170,7 @@ enum {
 
 #define RPC_IS_ACTIVATED(t)	test_bit(RPC_TASK_ACTIVE, &(t)->tk_runstate)
 
-#define RPC_SIGNALLED(t)	test_bit(RPC_TASK_SIGNALLED, &(t)->tk_runstate)
+#define RPC_SIGNALLED(t)	(READ_ONCE(task->tk_rpc_status) == -ERESTARTSYS)
 
 /*
  * Task priorities.

include/trace/events/sunrpc.h

@@ -360,8 +360,7 @@ TRACE_EVENT(rpc_request,
 		{ (1UL << RPC_TASK_ACTIVE), "ACTIVE" },			\
 		{ (1UL << RPC_TASK_NEED_XMIT), "NEED_XMIT" },		\
 		{ (1UL << RPC_TASK_NEED_RECV), "NEED_RECV" },		\
-		{ (1UL << RPC_TASK_MSG_PIN_WAIT), "MSG_PIN_WAIT" },	\
-		{ (1UL << RPC_TASK_SIGNALLED), "SIGNALLED" })
+		{ (1UL << RPC_TASK_MSG_PIN_WAIT), "MSG_PIN_WAIT" })
 
 DECLARE_EVENT_CLASS(rpc_task_running,
 

net/sunrpc/sched.c

@@ -864,8 +864,6 @@ void rpc_signal_task(struct rpc_task *task)
 	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(queue, task);