[PATCH] RDMA/cxgb3: test before subtraction on unsigned

[Roel Kluin <roel.kluin@gmail.com>]

I think there's someting wrong in iwch_post_send():

// vi drivers/infiniband/hw/cxgb3/iwch_qp.c +353
int iwch_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
                      struct ib_send_wr **bad_wr)
{
	...
        u32 num_wrs;
	...
        num_wrs = Q_FREECNT(qhp->wq.sq_rptr, qhp->wq.sq_wptr,
                  qhp->wq.sq_size_log2);
        if (num_wrs <= 0) {
                spin_unlock_irqrestore(&qhp->lock, flag);
                return -ENOMEM;
        }

// vi drivers/infiniband/hw/cxgb3/cxio_wr.h +50
#define Q_FREECNT(rptr,wptr,size_log2) ((1UL<<size_log2)-((wptr)-(rptr)))

Since num_wrs is unsigned, I think the test should occur before the subtraction,
right? please review.
------------------------------>8-------------8<---------------------------------
num_wrs is unsigned so test before the subtraction.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
---
diff --git a/drivers/infiniband/hw/cxgb3/iwch_qp.c b/drivers/infiniband/hw/cxgb3/iwch_qp.c
index 19661b2..1c6ebaf 100644
--- a/drivers/infiniband/hw/cxgb3/iwch_qp.c
+++ b/drivers/infiniband/hw/cxgb3/iwch_qp.c
@@ -369,12 +369,13 @@ int iwch_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
 		spin_unlock_irqrestore(&qhp->lock, flag);
 		return -EINVAL;
 	}
-	num_wrs = Q_FREECNT(qhp->wq.sq_rptr, qhp->wq.sq_wptr,
-		  qhp->wq.sq_size_log2);
-	if (num_wrs <= 0) {
+	if ((1UL << qhp->wq.sq_size_log2) + qhp->wq.sq_rptr <=
+			qhp->wq.sq_wptr) {
 		spin_unlock_irqrestore(&qhp->lock, flag);
 		return -ENOMEM;
 	}
+	num_wrs = Q_FREECNT(qhp->wq.sq_rptr, qhp->wq.sq_wptr,
+		  qhp->wq.sq_size_log2);
 	while (wr) {
 		if (num_wrs == 0) {
 			err = -ENOMEM;