IB/iser: Use beacon to indicate all completions were consumed

Avoid post_send counting (atomic) in the IO path just to keep track of
how many completions we need to consume.  Use a beacon post to indicate
that all prior posts completed.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
diff --git a/drivers/infiniband/ulp/iser/iser_initiator.c b/drivers/infiniband/ulp/iser/iser_initiator.c
index 359c0b8..ffbdf92 100644
--- a/drivers/infiniband/ulp/iser/iser_initiator.c
+++ b/drivers/infiniband/ulp/iser/iser_initiator.c
@@ -350,12 +350,10 @@
 		return 0;
 
 	/*
-	 * Check that there is one posted recv buffer (for the last login
-	 * response) and no posted send buffers left - they must have been
-	 * consumed during previous login phases.
+	 * Check that there is one posted recv buffer
+	 * (for the last login response).
 	 */
 	WARN_ON(ib_conn->post_recv_buf_count != 1);
-	WARN_ON(atomic_read(&ib_conn->post_send_buf_count) != 0);
 
 	if (session->discovery_sess) {
 		iser_info("Discovery session, re-using login RX buffer\n");
@@ -634,8 +632,6 @@
 		tx_desc = NULL;
 	}
 
-	atomic_dec(&ib_conn->post_send_buf_count);
-
 	if (tx_desc && tx_desc->type == ISCSI_TX_CONTROL) {
 		/* this arithmetic is legal by libiscsi dd_data allocation */
 		task = (void *) ((long)(void *)tx_desc -