If the sending queue has a task without ->rq_cong set at the front,
and then a number of tasks with ->rq_cong set such that they use
the entire congestion window, then the queue deadlocks. The first
entry cannot be processed until later entries complete.
This scenario has been seen with a client using UDP to access a server,
and the network connection breaking for a period of time - it doesn't
recover.
It never really makes sense for an ->rq_cong request to be on the ->sending
queue, but it can happen when a request is being retried, and finds
the transport if locked (XPRT_LOCKED). In this case we simple call
__xprt_put_cong() and the deadlock goes away.
Signed-off-by: NeilBrown <[email protected]>
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 1d4fe24..826fecf 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -68,6 +68,7 @@ static void xprt_init(struct rpc_xprt *xprt, struct net *net);
static void xprt_request_init(struct rpc_task *, struct rpc_xprt *);
static void xprt_connect_status(struct rpc_task *task);
static int __xprt_get_cong(struct rpc_xprt *, struct rpc_task *);
+static void __xprt_put_cong(struct rpc_xprt *, struct rpc_rqst *);
static void xprt_destroy(struct rpc_xprt *xprt);
static DEFINE_SPINLOCK(xprt_list_lock);
@@ -250,6 +251,8 @@ int xprt_reserve_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task)
}
xprt_clear_locked(xprt);
out_sleep:
+ if (req)
+ __xprt_put_cong(xprt, req);
dprintk("RPC: %5u failed to lock transport %p\n", task->tk_pid, xprt);
task->tk_timeout = 0;
task->tk_status = -EAGAIN;