xprtrdma: Fix backchannel allocation of extra rpcrdma_reps

The backchannel code uses rpcrdma_recv_buffer_put to add new reps
to the free rep list. This also decrements rb_recv_count, which
spoofs the receive overrun logic in rpcrdma_buffer_get_rep.

Commit 9b06688bc3b9 ("xprtrdma: Fix additional uses of
spin_lock_irqsave(rb_lock)") replaced the original open-coded
list_add with a call to rpcrdma_recv_buffer_put(), but then a year
later, commit 05c974669ece ("xprtrdma: Fix receive buffer
accounting") added rep accounting to rpcrdma_recv_buffer_put.
It was an oversight to let the backchannel continue to use this
function.

The fix this, let's combine the "add to free list" logic with
rpcrdma_create_rep.

Also, do not allocate RPCRDMA_MAX_BC_REQUESTS rpcrdma_reps in
rpcrdma_buffer_create and then allocate additional rpcrdma_reps in
rpcrdma_bc_setup_reps. Allocating the extra reps during backchannel
set-up is sufficient.

Fixes: 05c974669ece ("xprtrdma: Fix receive buffer accounting")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

3 files changed, 22 insertions, 24 deletions

diff --git a/net/sunrpc/xprtrdma/backchannel.c b/net/sunrpc/xprtrdma/backchannel.c
index 8b818bb3518a..256c67b433c1 100644
--- a/net/sunrpc/xprtrdma/backchannel.c
+++ b/net/sunrpc/xprtrdma/backchannel.c
@@ -74,21 +74,13 @@ out_fail:
 static int rpcrdma_bc_setup_reps(struct rpcrdma_xprt *r_xprt,
                                  unsigned int count)
 {
-        struct rpcrdma_rep *rep;
         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);
+                rc = rpcrdma_create_rep(r_xprt);
+                if (rc)
                         break;
-                }
-
-                rpcrdma_recv_buffer_put(rep);
         }
-
         return rc;
 }
 
diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
index 8607c029c0dd..6eecd9714051 100644
--- a/net/sunrpc/xprtrdma/verbs.c
+++ b/net/sunrpc/xprtrdma/verbs.c
@@ -1093,10 +1093,17 @@ rpcrdma_create_req(struct rpcrdma_xprt *r_xprt)
         return req;
 }
 
-struct rpcrdma_rep *
+/**
+ * rpcrdma_create_rep - Allocate an rpcrdma_rep object
+ * @r_xprt: controlling transport
+ *
+ * Returns 0 on success or a negative errno on failure.
+ */
+int
 rpcrdma_create_rep(struct rpcrdma_xprt *r_xprt)
 {
         struct rpcrdma_create_data_internal *cdata = &r_xprt->rx_data;
+        struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
         struct rpcrdma_rep *rep;
         int rc;
 
@@ -1121,12 +1128,18 @@ rpcrdma_create_rep(struct rpcrdma_xprt *r_xprt)
         rep->rr_recv_wr.wr_cqe = &rep->rr_cqe;
         rep->rr_recv_wr.sg_list = &rep->rr_rdmabuf->rg_iov;
         rep->rr_recv_wr.num_sge = 1;
-        return rep;
+
+        spin_lock(&buf->rb_lock);
+        list_add(&rep->rr_list, &buf->rb_recv_bufs);
+        spin_unlock(&buf->rb_lock);
+        return 0;
 
 out_free:
         kfree(rep);
 out:
-        return ERR_PTR(rc);
+        dprintk("RPC:       %s: reply buffer %d alloc failed\n",
+                __func__, rc);
+        return rc;
 }
 
 int
@@ -1167,17 +1180,10 @@ rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
         }
 
         INIT_LIST_HEAD(&buf->rb_recv_bufs);
-        for (i = 0; i < buf->rb_max_requests + RPCRDMA_MAX_BC_REQUESTS; i++) {
-                struct rpcrdma_rep *rep;
-
-                rep = rpcrdma_create_rep(r_xprt);
-                if (IS_ERR(rep)) {
-                        dprintk("RPC:       %s: reply buffer %d alloc failed\n",
-                                __func__, i);
-                        rc = PTR_ERR(rep);
+        for (i = 0; i <= buf->rb_max_requests; i++) {
+                rc = rpcrdma_create_rep(r_xprt);
+                if (rc)
                         goto out;
-                }
-                list_add(&rep->rr_list, &buf->rb_recv_bufs);
         }
 
         rc = rpcrdma_sendctxs_create(r_xprt);
diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
index 1342f743f1c4..3b63e61feae2 100644
--- a/net/sunrpc/xprtrdma/xprt_rdma.h
+++ b/net/sunrpc/xprtrdma/xprt_rdma.h
@@ -564,8 +564,8 @@ int rpcrdma_ep_post_recv(struct rpcrdma_ia *, struct rpcrdma_rep *);
  * Buffer calls - xprtrdma/verbs.c
  */
 struct rpcrdma_req *rpcrdma_create_req(struct rpcrdma_xprt *);
-struct rpcrdma_rep *rpcrdma_create_rep(struct rpcrdma_xprt *);
 void rpcrdma_destroy_req(struct rpcrdma_req *);
+int rpcrdma_create_rep(struct rpcrdma_xprt *r_xprt);
 int rpcrdma_buffer_create(struct rpcrdma_xprt *);
 void rpcrdma_buffer_destroy(struct rpcrdma_buffer *);
 struct rpcrdma_sendctx *rpcrdma_sendctx_get_locked(struct rpcrdma_buffer *buf);