On Mon, 2018-12-17 at 11:39 -0500, Chuck Lever wrote:
> Transport disconnect processing does a "wake pending tasks" at
> various points.
>
> Suppose an RPC Reply is being processed. The RPC task that Reply
> goes with is waiting on the pending queue. If a disconnect wake-up
> happens before reply processing is done, that reply, even if it is
> good, is thrown away, and the RPC has to be sent again.
>
> This window apparently does not exist for socket transports because
> there is a lock held while a reply is being received which prevents
> the wake-up call until after reply processing is done.
>
> To resolve this, all RPC replies being processed on an RPC-over-RDMA
> transport have to complete before pending tasks are awoken due to a
> transport disconnect.
>
> Callers that already hold the transport write lock may invoke
> ->ops->close directly. Others use a generic helper that schedules
> a close when the write lock can be taken safely.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> include/linux/sunrpc/xprt.h | 1 +
> net/sunrpc/xprt.c | 19
> +++++++++++++++++++
> net/sunrpc/xprtrdma/backchannel.c | 13 +++++++------
> net/sunrpc/xprtrdma/svc_rdma_backchannel.c | 8 +++++---
> net/sunrpc/xprtrdma/transport.c | 16 ++++++++++------
> net/sunrpc/xprtrdma/verbs.c | 5 ++---
> 6 files changed, 44 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/sunrpc/xprt.h
> b/include/linux/sunrpc/xprt.h
> index a4ab4f8..ee94ed0 100644
> --- a/include/linux/sunrpc/xprt.h
> +++ b/include/linux/sunrpc/xprt.h
> @@ -401,6 +401,7 @@ static inline __be32
> *xprt_skip_transport_header(struct rpc_xprt *xprt, __be32 *
> bool xprt_request_get_cong(struct rpc_xprt *xprt,
> struct rpc_rqst *req);
> void xprt_disconnect_done(struct rpc_xprt *xprt);
> void xprt_force_disconnect(struct rpc_xprt *xprt);
> +void xprt_disconnect_nowake(struct rpc_xprt *xprt);
> void xprt_conditional_disconnect(struct rpc_xprt
> *xprt, unsigned int cookie);
>
> bool xprt_lock_connect(struct rpc_xprt *, struct
> rpc_task *, void *);
> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
> index ce92700..afe412e 100644
> --- a/net/sunrpc/xprt.c
> +++ b/net/sunrpc/xprt.c
> @@ -685,6 +685,25 @@ void xprt_force_disconnect(struct rpc_xprt
> *xprt)
> }
> EXPORT_SYMBOL_GPL(xprt_force_disconnect);
>
> +/**
> + * xprt_disconnect_nowake - force a call to xprt->ops->close
> + * @xprt: transport to disconnect
> + *
> + * The caller must ensure that xprt_wake_pending_tasks() is
> + * called later.
> + */
> +void xprt_disconnect_nowake(struct rpc_xprt *xprt)
> +{
> + /* Don't race with the test_bit() in xprt_clear_locked() */
> + spin_lock_bh(&xprt->transport_lock);
> + set_bit(XPRT_CLOSE_WAIT, &xprt->state);
> + /* Try to schedule an autoclose RPC call */
> + if (test_and_set_bit(XPRT_LOCKED, &xprt->state) == 0)
> + queue_work(xprtiod_workqueue, &xprt->task_cleanup);
> + spin_unlock_bh(&xprt->transport_lock);
> +}
> +EXPORT_SYMBOL_GPL(xprt_disconnect_nowake);
> +
We shouldn't need both xprt_disconnect_nowake() and
xprt_force_disconnect() to be exported given that you can build the
latter from the former + xprt_wake_pending_tasks() (which is also
already exported).
> static unsigned int
> xprt_connect_cookie(struct rpc_xprt *xprt)
> {
> diff --git a/net/sunrpc/xprtrdma/backchannel.c
> b/net/sunrpc/xprtrdma/backchannel.c
> index 2cb07a3..5d462e8 100644
> --- a/net/sunrpc/xprtrdma/backchannel.c
> +++ b/net/sunrpc/xprtrdma/backchannel.c
> @@ -193,14 +193,15 @@ static int rpcrdma_bc_marshal_reply(struct
> rpc_rqst *rqst)
> */
> int xprt_rdma_bc_send_reply(struct rpc_rqst *rqst)
> {
> - struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(rqst->rq_xprt);
> + struct rpc_xprt *xprt = rqst->rq_xprt;
> + struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
> struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
> int rc;
>
> - if (!xprt_connected(rqst->rq_xprt))
> - goto drop_connection;
> + if (!xprt_connected(xprt))
> + return -ENOTCONN;
>
> - if (!xprt_request_get_cong(rqst->rq_xprt, rqst))
> + if (!xprt_request_get_cong(xprt, rqst))
> return -EBADSLT;
>
> rc = rpcrdma_bc_marshal_reply(rqst);
> @@ -215,7 +216,7 @@ int xprt_rdma_bc_send_reply(struct rpc_rqst
> *rqst)
> if (rc != -ENOTCONN)
> return rc;
> drop_connection:
> - xprt_disconnect_done(rqst->rq_xprt);
> + xprt->ops->close(xprt);
Why use an indirect call here? Is this ever going to be different to
xprt_rdma_close()?
> return -ENOTCONN;
> }
>
> @@ -338,7 +339,7 @@ void rpcrdma_bc_receive_call(struct rpcrdma_xprt
> *r_xprt,
>
> out_overflow:
> pr_warn("RPC/RDMA backchannel overflow\n");
> - xprt_disconnect_done(xprt);
> + xprt_disconnect_nowake(xprt);
> /* This receive buffer gets reposted automatically
> * when the connection is re-established.
> */
> diff --git a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> index f3c147d..b908f2c 100644
> --- a/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> +++ b/net/sunrpc/xprtrdma/svc_rdma_backchannel.c
> @@ -200,11 +200,10 @@ static int svc_rdma_bc_sendto(struct
> svcxprt_rdma *rdma,
> svc_rdma_send_ctxt_put(rdma, ctxt);
> goto drop_connection;
> }
> - return rc;
> + return 0;
>
> drop_connection:
> dprintk("svcrdma: failed to send bc call\n");
> - xprt_disconnect_done(xprt);
> return -ENOTCONN;
> }
>
> @@ -225,8 +224,11 @@ static int svc_rdma_bc_sendto(struct
> svcxprt_rdma *rdma,
>
> ret = -ENOTCONN;
> rdma = container_of(sxprt, struct svcxprt_rdma, sc_xprt);
> - if (!test_bit(XPT_DEAD, &sxprt->xpt_flags))
> + if (!test_bit(XPT_DEAD, &sxprt->xpt_flags)) {
> ret = rpcrdma_bc_send_request(rdma, rqst);
> + if (ret == -ENOTCONN)
> + svc_close_xprt(sxprt);
> + }
>
> mutex_unlock(&sxprt->xpt_mutex);
>
> diff --git a/net/sunrpc/xprtrdma/transport.c
> b/net/sunrpc/xprtrdma/transport.c
> index 91c476a..a16296b 100644
> --- a/net/sunrpc/xprtrdma/transport.c
> +++ b/net/sunrpc/xprtrdma/transport.c
> @@ -453,13 +453,13 @@
>
> if (test_and_clear_bit(RPCRDMA_IAF_REMOVING, &ia->ri_flags)) {
> rpcrdma_ia_remove(ia);
> - return;
> + goto out;
> }
> +
> if (ep->rep_connected == -ENODEV)
> return;
> if (ep->rep_connected > 0)
> xprt->reestablish_timeout = 0;
> - xprt_disconnect_done(xprt);
> rpcrdma_ep_disconnect(ep, ia);
>
> /* Prepare @xprt for the next connection by reinitializing
> @@ -467,6 +467,10 @@
> */
> r_xprt->rx_buf.rb_credits = 1;
> xprt->cwnd = RPC_CWNDSHIFT;
> +
> +out:
> + ++xprt->connect_cookie;
> + xprt_disconnect_done(xprt);
> }
>
> /**
> @@ -515,7 +519,7 @@
> static void
> xprt_rdma_timer(struct rpc_xprt *xprt, struct rpc_task *task)
> {
> - xprt_force_disconnect(xprt);
> + xprt_disconnect_nowake(xprt);
> }
>
> /**
> @@ -717,7 +721,7 @@
> #endif /* CONFIG_SUNRPC_BACKCHANNEL */
>
> if (!xprt_connected(xprt))
> - goto drop_connection;
> + return -ENOTCONN;
>
> if (!xprt_request_get_cong(xprt, rqst))
> return -EBADSLT;
> @@ -749,8 +753,8 @@
> if (rc != -ENOTCONN)
> return rc;
> drop_connection:
> - xprt_disconnect_done(xprt);
> - return -ENOTCONN; /* implies disconnect */
> + xprt_rdma_close(xprt);
> + return -ENOTCONN;
> }
>
> void xprt_rdma_print_stats(struct rpc_xprt *xprt, struct seq_file
> *seq)
> diff --git a/net/sunrpc/xprtrdma/verbs.c
> b/net/sunrpc/xprtrdma/verbs.c
> index 9a0a765..38a757c 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -252,7 +252,7 @@ static void rpcrdma_xprt_drain(struct
> rpcrdma_xprt *r_xprt)
> #endif
> set_bit(RPCRDMA_IAF_REMOVING, &ia->ri_flags);
> ep->rep_connected = -ENODEV;
> - xprt_force_disconnect(xprt);
> + xprt_disconnect_nowake(xprt);
> wait_for_completion(&ia->ri_remove_done);
>
> ia->ri_id = NULL;
> @@ -280,10 +280,9 @@ static void rpcrdma_xprt_drain(struct
> rpcrdma_xprt *r_xprt)
> ep->rep_connected = -EAGAIN;
> goto disconnected;
> case RDMA_CM_EVENT_DISCONNECTED:
> - ++xprt->connect_cookie;
> ep->rep_connected = -ECONNABORTED;
> disconnected:
> - xprt_force_disconnect(xprt);
> + xprt_disconnect_nowake(xprt);
> wake_up_all(&ep->rep_connect_wait);
> break;
> default:
>
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
