[PATCH] SUNRPC: Set tk_rpc_status when RPC_TASK_SIGNALLED is detected

[Li Lingfeng <lilingfeng3@huawei.com>]

Commit 39494194f93b("SUNRPC: Fix races with rpc_killall_tasks()") adds
rpc_task_set_rpc_status before setting RPC_TASK_SIGNALLED in
rpc_signal_task, ensuring that rpc_status is definitely set when
RPC_TASK_SIGNALLED is set.
Therefore, it seems unnecessary to set rpc_status again after detecting
RPC_TASK_SIGNALLED in rpc_check_timeout.

However, in some exceptional cases, invalid and endlessly looping
rpc_tasks may be generated. The rpc_call_rpcerror in rpc_check_timeout can
timely terminate such rpc_tasks. Removing rpc_call_rpcerror may cause the
rpc_task to fall into an infinite loop.

For example, in the following situation:
nfs4_close_done
 // get err from server
 nfs4_async_handle_exception
 // goto out_restart
                            // umount -f
                            nfs_umount_begin
                             rpc_killall_tasks
                              rpc_signal_task
                               rpc_task_set_rpc_status
                                task->tk_rpc_status = -ERESTARTSYS
                                set_bit
                                // set RPC_TASK_SIGNALLED to tk_runstate
 rpc_restart_call_prepare
  __rpc_restart_call
   task->tk_rpc_status = 0
   // clear tk_rpc_status
  ...
  rpc_prepare_task
   nfs4_close_prepare
    nfs4_setup_sequence
     rpc_call_start
      task->tk_action = call_start

At this point, an rpc_task with RPC_TASK_SIGNALLED set but tk_rpc_status
as 0 will be generated. This rpc_task will fall into the following loop:
call_encode --> call_transmit --> call_transmit_status --> call_status
--> call_encode.

Since RPC_TASK_SIGNALLED is set, no request will be sent in call_transmit.
Similarly, since RPC_TASK_SIGNALLED is set, rq_majortimeo will not be
updated in call_status --> rpc_check_timeout, which will cause -ETIMEDOUT
to be directly set to tk_status in call_transmit_status -->
xprt_request_wait_receive --> xprt_wait_for_reply_request_def -->
rpc_sleep_on_timeout --> __rpc_sleep_on_priority_timeout.

Here is the state and loop process of the rpc_task:
tk_runstate:
RPC_TASK_RUNNING RPC_TASK_ACTIVE RPC_TASK_NEED_RECV RPC_TASK_SIGNALLED
tk_xprt->state:
XPRT_CONNECTED XPRT_BOUND
tk_flags
RPC_TASK_ASYNC RPC_TASK_MOVEABLE RPC_TASK_DYNAMIC RPC_TASK_SOFT
RPC_TASK_NO_RETRANS_TIMEOUT RPC_TASK_CRED_NOREF

call_encode
 xprt_request_enqueue_transmit
  set_bit // RPC_TASK_NEED_XMIT
 task->tk_action = call_transmit

call_transmit
 task->tk_action = call_transmit_status
 xprt_transmit
  xprt_request_transmit
   // check RPC_TASK_SIGNALLED and goto out_dequeue
   xprt_request_dequeue_transmit
    xprt_request_dequeue_transmit_locked
     test_and_clear_bit // RPC_TASK_NEED_XMIT

call_transmit_status
 task->tk_action = call_status
 xprt_request_wait_receive
  xprt_wait_for_reply_request_def
   xprt_request_timeout // get timeout
    req->rq_majortimeo // rq_majortimeo will not be updated
   rpc_sleep_on_timeout
    __rpc_sleep_on_priority_timeout
     task->tk_status = -ETIMEDOUT // set ETIMEDOUT

call_status
 task->tk_action = call_encode
 rpc_check_timeout
  // check RPC_TASK_SIGNALLED and skip xprt_reset_majortimeo

Fix it by adding rpc_call_rpcerror back.

Fixes: 39494194f93b ("SUNRPC: Fix races with rpc_killall_tasks()")
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
---
 net/sunrpc/clnt.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 0090162ee8c3..0acdff19a37c 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -2509,8 +2509,10 @@ rpc_check_timeout(struct rpc_task *task)
 {
 	struct rpc_clnt	*clnt = task->tk_client;
 
-	if (RPC_SIGNALLED(task))
+	if (RPC_SIGNALLED(task)) {
+		rpc_call_rpcerror(task, -ERESTARTSYS);
 		return;
+	}
 
 	if (xprt_adjust_timeout(task->tk_rqstp) == 0)
 		return;
-- 
2.31.1