提交 29807318 编写于 作者: N Neil Brown 提交者: Trond Myklebust

SUNRPC: never enqueue a ->rq_cong request on ->sending

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: NNeilBrown <neilb@suse.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>
上级 6f02dc88
......@@ -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;
......
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