xprtrdma: Pre-allocate backward rpc_rqst and send/receive buffers

xprtrdma's backward direction send and receive buffers are the same
size as the forechannel's inline threshold, and must be pre-
registered.

The consumer has no control over which receive buffer the adapter
chooses to catch an incoming backwards-direction call. Any receive
buffer can be used for either a forward reply or a backward call.
Thus both types of RPC message must all be the same size.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Tested-By: Devesh Sharma <devesh.sharma@avagotech.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

1 files changed, 206 insertions, 0 deletions

diff --git a/net/sunrpc/xprtrdma/backchannel.c b/net/sunrpc/xprtrdma/backchannel.c
new file mode 100644
index 000000000000..3d01b328f777
--- /dev/null
+++ b/net/sunrpc/xprtrdma/backchannel.c
@@ -0,0 +1,206 @@
+/*
+ * Copyright (c) 2015 Oracle.  All rights reserved.
+ *
+ * Support for backward direction RPCs on RPC/RDMA.
+ */
+
+#include <linux/module.h>
+
+#include "xprt_rdma.h"
+
+#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
+# define RPCDBG_FACILITY	RPCDBG_TRANS
+#endif
+
+static void rpcrdma_bc_free_rqst(struct rpcrdma_xprt *r_xprt,
+				 struct rpc_rqst *rqst)
+{
+	struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
+	struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
+
+	spin_lock(&buf->rb_reqslock);
+	list_del(&req->rl_all);
+	spin_unlock(&buf->rb_reqslock);
+
+	rpcrdma_destroy_req(&r_xprt->rx_ia, req);
+
+	kfree(rqst);
+}
+
+static int rpcrdma_bc_setup_rqst(struct rpcrdma_xprt *r_xprt,
+				 struct rpc_rqst *rqst)
+{
+	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
+	struct rpcrdma_regbuf *rb;
+	struct rpcrdma_req *req;
+	struct xdr_buf *buf;
+	size_t size;
+
+	req = rpcrdma_create_req(r_xprt);
+	if (!req)
+		return -ENOMEM;
+	req->rl_backchannel = true;
+
+	size = RPCRDMA_INLINE_WRITE_THRESHOLD(rqst);
+	rb = rpcrdma_alloc_regbuf(ia, size, GFP_KERNEL);
+	if (IS_ERR(rb))
+		goto out_fail;
+	req->rl_rdmabuf = rb;
+
+	size += RPCRDMA_INLINE_READ_THRESHOLD(rqst);
+	rb = rpcrdma_alloc_regbuf(ia, size, GFP_KERNEL);
+	if (IS_ERR(rb))
+		goto out_fail;
+	rb->rg_owner = req;
+	req->rl_sendbuf = rb;
+	/* so that rpcr_to_rdmar works when receiving a request */
+	rqst->rq_buffer = (void *)req->rl_sendbuf->rg_base;
+
+	buf = &rqst->rq_snd_buf;
+	buf->head[0].iov_base = rqst->rq_buffer;
+	buf->head[0].iov_len = 0;
+	buf->tail[0].iov_base = NULL;
+	buf->tail[0].iov_len = 0;
+	buf->page_len = 0;
+	buf->len = 0;
+	buf->buflen = size;
+
+	return 0;
+
+out_fail:
+	rpcrdma_bc_free_rqst(r_xprt, rqst);
+	return -ENOMEM;
+}
+
+/* Allocate and add receive buffers to the rpcrdma_buffer's
+ * existing list of rep's. These are released when the
+ * transport is destroyed.
+ */
+static int rpcrdma_bc_setup_reps(struct rpcrdma_xprt *r_xprt,
+				 unsigned int count)
+{
+	struct rpcrdma_buffer *buffers = &r_xprt->rx_buf;
+	struct rpcrdma_rep *rep;
+	unsigned long flags;
+	int rc = 0;
+
+	while (count--) {
+		rep = rpcrdma_create_rep(r_xprt);
+		if (IS_ERR(rep)) {
+			pr_err("RPC:       %s: reply buffer alloc failed\n",
+			       __func__);
+			rc = PTR_ERR(rep);
+			break;
+		}
+
+		spin_lock_irqsave(&buffers->rb_lock, flags);
+		list_add(&rep->rr_list, &buffers->rb_recv_bufs);
+		spin_unlock_irqrestore(&buffers->rb_lock, flags);
+	}
+
+	return rc;
+}
+
+/**
+ * xprt_rdma_bc_setup - Pre-allocate resources for handling backchannel requests
+ * @xprt: transport associated with these backchannel resources
+ * @reqs: number of concurrent incoming requests to expect
+ *
+ * Returns 0 on success; otherwise a negative errno
+ */
+int xprt_rdma_bc_setup(struct rpc_xprt *xprt, unsigned int reqs)
+{
+	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
+	struct rpcrdma_buffer *buffer = &r_xprt->rx_buf;
+	struct rpc_rqst *rqst;
+	unsigned int i;
+	int rc;
+
+	/* The backchannel reply path returns each rpc_rqst to the
+	 * bc_pa_list _after_ the reply is sent. If the server is
+	 * faster than the client, it can send another backward
+	 * direction request before the rpc_rqst is returned to the
+	 * list. The client rejects the request in this case.
+	 *
+	 * Twice as many rpc_rqsts are prepared to ensure there is
+	 * always an rpc_rqst available as soon as a reply is sent.
+	 */
+	for (i = 0; i < (reqs << 1); i++) {
+		rqst = kzalloc(sizeof(*rqst), GFP_KERNEL);
+		if (!rqst) {
+			pr_err("RPC:       %s: Failed to create bc rpc_rqst\n",
+			       __func__);
+			goto out_free;
+		}
+
+		rqst->rq_xprt = &r_xprt->rx_xprt;
+		INIT_LIST_HEAD(&rqst->rq_list);
+		INIT_LIST_HEAD(&rqst->rq_bc_list);
+
+		if (rpcrdma_bc_setup_rqst(r_xprt, rqst))
+			goto out_free;
+
+		spin_lock_bh(&xprt->bc_pa_lock);
+		list_add(&rqst->rq_bc_pa_list, &xprt->bc_pa_list);
+		spin_unlock_bh(&xprt->bc_pa_lock);
+	}
+
+	rc = rpcrdma_bc_setup_reps(r_xprt, reqs);
+	if (rc)
+		goto out_free;
+
+	rc = rpcrdma_ep_post_extra_recv(r_xprt, reqs);
+	if (rc)
+		goto out_free;
+
+	buffer->rb_bc_srv_max_requests = reqs;
+	request_module("svcrdma");
+
+	return 0;
+
+out_free:
+	xprt_rdma_bc_destroy(xprt, reqs);
+
+	pr_err("RPC:       %s: setup backchannel transport failed\n", __func__);
+	return -ENOMEM;
+}
+
+/**
+ * xprt_rdma_bc_destroy - Release resources for handling backchannel requests
+ * @xprt: transport associated with these backchannel resources
+ * @reqs: number of incoming requests to destroy; ignored
+ */
+void xprt_rdma_bc_destroy(struct rpc_xprt *xprt, unsigned int reqs)
+{
+	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
+	struct rpc_rqst *rqst, *tmp;
+
+	spin_lock_bh(&xprt->bc_pa_lock);
+	list_for_each_entry_safe(rqst, tmp, &xprt->bc_pa_list, rq_bc_pa_list) {
+		list_del(&rqst->rq_bc_pa_list);
+		spin_unlock_bh(&xprt->bc_pa_lock);
+
+		rpcrdma_bc_free_rqst(r_xprt, rqst);
+
+		spin_lock_bh(&xprt->bc_pa_lock);
+	}
+	spin_unlock_bh(&xprt->bc_pa_lock);
+}
+
+/**
+ * xprt_rdma_bc_free_rqst - Release a backchannel rqst
+ * @rqst: request to release
+ */
+void xprt_rdma_bc_free_rqst(struct rpc_rqst *rqst)
+{
+	struct rpc_xprt *xprt = rqst->rq_xprt;
+
+	smp_mb__before_atomic();
+	WARN_ON_ONCE(!test_bit(RPC_BC_PA_IN_USE, &rqst->rq_bc_pa_state));
+	clear_bit(RPC_BC_PA_IN_USE, &rqst->rq_bc_pa_state);
+	smp_mb__after_atomic();
+
+	spin_lock_bh(&xprt->bc_pa_lock);
+	list_add_tail(&rqst->rq_bc_pa_list, &xprt->bc_pa_list);
+	spin_unlock_bh(&xprt->bc_pa_lock);
+}