IB/iser: Fix possible SQ overflow

Fix a regression was introduced in commit 6df5a128 ("IB/iser:
Suppress scsi command send completions").

The sig_count was wrongly set to be static variable, thus it is
possible that we won't reach to (sig_count % ISER_SIGNAL_BATCH) == 0
condition (due to races) and the send queue will be overflowed.

Instead keep sig_count per connection. We don't need it to be atomic
as we are safe under the iscsi session frwd_lock taken by libiscsi on
the queuecommand path.

Fixes: 6df5a128 ("IB/iser: Suppress scsi command send completions")
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/iser/iscsi_iser.h

@@ -437,6 +437,7 @@ struct fast_reg_descriptor {
  * @cma_id:              rdma_cm connection maneger handle
  * @qp:                  Connection Queue-pair
  * @post_recv_buf_count: post receive counter
+ * @sig_count:           send work request signal count
  * @rx_wr:               receive work request for batch posts
  * @device:              reference to iser device
  * @comp:                iser completion context
@@ -457,6 +458,7 @@ struct ib_conn {
 	struct rdma_cm_id           *cma_id;
 	struct ib_qp	            *qp;
 	int                          post_recv_buf_count;
+	u8                           sig_count;
 	struct ib_recv_wr	     rx_wr[ISER_MIN_POSTED_RX];
 	struct iser_device          *device;
 	struct iser_comp	    *comp;

drivers/infiniband/ulp/iser/iser_initiator.c

@@ -369,7 +369,7 @@ static int iser_post_rx_bufs(struct iscsi_conn *conn, struct iscsi_hdr *req)
 	return 0;
 }
 
-static inline bool iser_signal_comp(int sig_count)
+static inline bool iser_signal_comp(u8 sig_count)
 {
 	return ((sig_count % ISER_SIGNAL_CMD_COUNT) == 0);
 }
@@ -388,7 +388,7 @@ int iser_send_command(struct iscsi_conn *conn,
 	struct iscsi_scsi_req *hdr = (struct iscsi_scsi_req *)task->hdr;
 	struct scsi_cmnd *sc  =  task->sc;
 	struct iser_tx_desc *tx_desc = &iser_task->desc;
-	static unsigned sig_count;
+	u8 sig_count = ++iser_conn->ib_conn.sig_count;
 
 	edtl = ntohl(hdr->data_length);
 
@@ -435,7 +435,7 @@ int iser_send_command(struct iscsi_conn *conn,
 	iser_task->status = ISER_TASK_STATUS_STARTED;
 
 	err = iser_post_send(&iser_conn->ib_conn, tx_desc,
-			     iser_signal_comp(++sig_count));
+			     iser_signal_comp(sig_count));
 	if (!err)
 		return 0;