9P/RDMA: count posted buffers without a pending request

In rdma_request():

If an error occurs between posting the recv and the send,
there will be a reply context posted without a pending
request.
Since there is no way to "un-post" it, we remember it and
skip post_recv() for the next request.

Signed-off-by: Simon Derr <simon.derr@bull.net>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

2 files changed, 34 insertions, 3 deletions

diff --git a/net/9p/client.c b/net/9p/client.c
index db5bf2480a33..d18a0b22f62c 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -656,8 +656,10 @@ static int p9_client_flush(struct p9_client *c, struct p9_req_t *oldreq)
                 return PTR_ERR(req);
 
 
-        /* if we haven't received a response for oldreq,
-           remove it from the list. */
+        /*
+         * if we haven't received a response for oldreq,
+         * remove it from the list.
+         */
         spin_lock(&c->lock);
         if (oldreq->status == REQ_STATUS_FLSH)
                 list_del(&oldreq->req_list);
diff --git a/net/9p/trans_rdma.c b/net/9p/trans_rdma.c
index 926e72d00e57..8f68df5d2973 100644
--- a/net/9p/trans_rdma.c
+++ b/net/9p/trans_rdma.c
@@ -74,6 +74,8 @@
  * @sq_sem: Semaphore for the SQ
  * @rq_depth: The depth of the Receive Queue.
  * @rq_sem: Semaphore for the RQ
+ * @excess_rc : Amount of posted Receive Contexts without a pending request.
+ *              See rdma_request()
  * @addr: The remote peer's address
  * @req_lock: Protects the active request list
  * @cm_done: Completion event for connection management tracking
@@ -99,6 +101,7 @@ struct p9_trans_rdma {
         struct semaphore sq_sem;
         int rq_depth;
         struct semaphore rq_sem;
+        atomic_t excess_rc;
         struct sockaddr_in addr;
         spinlock_t req_lock;
 
@@ -426,6 +429,26 @@ static int rdma_request(struct p9_client *client, struct p9_req_t *req)
         struct p9_rdma_context *c = NULL;
         struct p9_rdma_context *rpl_context = NULL;
 
+        /* When an error occurs between posting the recv and the send,
+         * there will be a receive context posted without a pending request.
+         * Since there is no way to "un-post" it, we remember it and skip
+         * post_recv() for the next request.
+         * So here,
+         * see if we are this `next request' and need to absorb an excess rc.
+         * If yes, then drop and free our own, and do not recv_post().
+         **/
+        if (unlikely(atomic_read(&rdma->excess_rc) > 0)) {
+                if ((atomic_sub_return(1, &rdma->excess_rc) >= 0)) {
+                        /* Got one ! */
+                        kfree(req->rc);
+                        req->rc = NULL;
+                        goto dont_need_post_recv;
+                } else {
+                        /* We raced and lost. */
+                        atomic_inc(&rdma->excess_rc);
+                }
+        }
+
         /* Allocate an fcall for the reply */
         rpl_context = kmalloc(sizeof *rpl_context, GFP_NOFS);
         if (!rpl_context) {
@@ -451,10 +474,10 @@ static int rdma_request(struct p9_client *client, struct p9_req_t *req)
                 p9_debug(P9_DEBUG_FCALL, "POST RECV failed\n");
                 goto recv_error;
         }
-
         /* remove posted receive buffer from request structure */
         req->rc = NULL;
 
+dont_need_post_recv:
         /* Post the request */
         c = kmalloc(sizeof *c, GFP_NOFS);
         if (!c) {
@@ -499,6 +522,11 @@ static int rdma_request(struct p9_client *client, struct p9_req_t *req)
  send_error:
         kfree(c);
         p9_debug(P9_DEBUG_ERROR, "Error %d in rdma_request()\n", err);
+
+        /* Ach.
+         *  We did recv_post(), but not send. We have one recv_post in excess.
+         */
+        atomic_inc(&rdma->excess_rc);
         return err;
 
  /* Handle errors that happened during or while preparing post_recv(): */
@@ -549,6 +577,7 @@ static struct p9_trans_rdma *alloc_rdma(struct p9_rdma_opts *opts)
         init_completion(&rdma->cm_done);
         sema_init(&rdma->sq_sem, rdma->sq_depth);
         sema_init(&rdma->rq_sem, rdma->rq_depth);
+        atomic_set(&rdma->excess_rc, 0);
 
         return rdma;
 }