[PATCH -next] SUNRPC: Clean XPRT_CONGESTED of xprt->state when rpc task is killed

[Bixuan Cui <cuibixuan@xxxxxxxxxxxxxxxxx>]

When the values of tcp_max_slot_table_entries and
sunrpc.tcp_slot_table_entries are lower than the number of rpc tasks,
xprt_dynamic_alloc_slot() in xprt_alloc_slot() will return -EAGAIN, and
then set xprt->state to XPRT_CONGESTED:
  xprt_retry_reserve
    ->xprt_do_reserve
      ->xprt_alloc_slot
        ->xprt_dynamic_alloc_slot // return -EAGAIN and task->tk_rqstp is NULL
          ->xprt_add_backlog // set_bit(XPRT_CONGESTED, &xprt->state);

When rpc task is killed, XPRT_CONGESTED bit of xprt->state will not be
cleaned up and nfs hangs:
  rpc_exit_task
    ->xprt_release // if (req == NULL) is true, then XPRT_CONGESTED
		   // bit not clean

Add xprt_wake_up_backlog(xprt) to clean XPRT_CONGESTED bit in
xprt_release().

Signed-off-by: Bixuan Cui <cuibixuan@xxxxxxxxxxxxxxxxx>
Signed-off-by: Xiaohui Pei <xiaoh.peixh@xxxxxxxxxxxxxxx>
---
 net/sunrpc/xprt.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index a02de2b..70d11ae 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1952,6 +1952,7 @@ void xprt_release(struct rpc_task *task)
 	if (req == NULL) {
 		if (task->tk_client) {
 			xprt = task->tk_xprt;
+			xprt_wake_up_backlog(xprt);
 			xprt_release_write(xprt, task);
 		}
 		return;
-- 
1.8.3.1