RDMA/cxgb4: Serialize calls to CQ's comp_handler

Commit 01e7da6 ("RDMA/cxgb4: Make sure flush CQ entries are
collected on connection close") introduced a potential problem where a
CQ's comp_handler can get called simultaneously from different places
in the iw_cxgb4 driver.  This does not comply with
Documentation/infiniband/core_locking.txt, which states that at a
given point of time, there should be only one callback per CQ should
be active.

This problem was reported by Parav Pandit <Parav.Pandit@Emulex.Com>.
Based on discussion between Parav Pandit and Steve Wise, this patch
fixes the above problem by serializing the calls to a CQ's
comp_handler using a spin_lock.

Reported-by: Parav Pandit <Parav.Pandit@Emulex.Com>
Signed-off-by: Kumar Sanghvi <kumaras@chelsio.com>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/hw/cxgb4/cq.c

@@ -818,6 +818,7 @@ struct ib_cq *c4iw_create_cq(struct ib_device *ibdev, int entries,
 	chp->cq.size--;				/* status page */
 	chp->ibcq.cqe = entries - 2;
 	spin_lock_init(&chp->lock);
+	spin_lock_init(&chp->comp_handler_lock);
 	atomic_set(&chp->refcnt, 1);
 	init_waitqueue_head(&chp->wait);
 	ret = insert_handle(rhp, &rhp->cqidr, chp, chp->cq.cqid);

drivers/infiniband/hw/cxgb4/ev.c

@@ -42,6 +42,7 @@ static void post_qp_event(struct c4iw_dev *dev, struct c4iw_cq *chp,
 {
 	struct ib_event event;
 	struct c4iw_qp_attributes attrs;
+	unsigned long flag;
 
 	if ((qhp->attr.state == C4IW_QP_STATE_ERROR) ||
 	    (qhp->attr.state == C4IW_QP_STATE_TERMINATE)) {
@@ -72,7 +73,9 @@ static void post_qp_event(struct c4iw_dev *dev, struct c4iw_cq *chp,
 	if (qhp->ibqp.event_handler)
 		(*qhp->ibqp.event_handler)(&event, qhp->ibqp.qp_context);
 
+	spin_lock_irqsave(&chp->comp_handler_lock, flag);
 	(*chp->ibcq.comp_handler)(&chp->ibcq, chp->ibcq.cq_context);
+	spin_unlock_irqrestore(&chp->comp_handler_lock, flag);
 }
 
 void c4iw_ev_dispatch(struct c4iw_dev *dev, struct t4_cqe *err_cqe)
@@ -183,11 +186,14 @@ void c4iw_ev_dispatch(struct c4iw_dev *dev, struct t4_cqe *err_cqe)
 int c4iw_ev_handler(struct c4iw_dev *dev, u32 qid)
 {
 	struct c4iw_cq *chp;
+	unsigned long flag;
 
 	chp = get_chp(dev, qid);
-	if (chp)
+	if (chp) {
+		spin_lock_irqsave(&chp->comp_handler_lock, flag);
 		(*chp->ibcq.comp_handler)(&chp->ibcq, chp->ibcq.cq_context);
-	else
+		spin_unlock_irqrestore(&chp->comp_handler_lock, flag);
+	} else
 		PDBG("%s unknown cqid 0x%x\n", __func__, qid);
 	return 0;
 }

drivers/infiniband/hw/cxgb4/iw_cxgb4.h

@@ -309,6 +309,7 @@ struct c4iw_cq {
 	struct c4iw_dev *rhp;
 	struct t4_cq cq;
 	spinlock_t lock;
+	spinlock_t comp_handler_lock;
 	atomic_t refcnt;
 	wait_queue_head_t wait;
 };

drivers/infiniband/hw/cxgb4/qp.c

@@ -941,8 +941,11 @@ static void __flush_qp(struct c4iw_qp *qhp, struct c4iw_cq *rchp,
 	flushed = c4iw_flush_rq(&qhp->wq, &rchp->cq, count);
 	spin_unlock(&qhp->lock);
 	spin_unlock_irqrestore(&rchp->lock, flag);
-	if (flushed)
+	if (flushed) {
+		spin_lock_irqsave(&rchp->comp_handler_lock, flag);
 		(*rchp->ibcq.comp_handler)(&rchp->ibcq, rchp->ibcq.cq_context);
+		spin_unlock_irqrestore(&rchp->comp_handler_lock, flag);
+	}
 
 	/* locking hierarchy: cq lock first, then qp lock. */
 	spin_lock_irqsave(&schp->lock, flag);
@@ -952,25 +955,33 @@ static void __flush_qp(struct c4iw_qp *qhp, struct c4iw_cq *rchp,
 	flushed = c4iw_flush_sq(&qhp->wq, &schp->cq, count);
 	spin_unlock(&qhp->lock);
 	spin_unlock_irqrestore(&schp->lock, flag);
-	if (flushed)
+	if (flushed) {
+		spin_lock_irqsave(&schp->comp_handler_lock, flag);
 		(*schp->ibcq.comp_handler)(&schp->ibcq, schp->ibcq.cq_context);
+		spin_unlock_irqrestore(&schp->comp_handler_lock, flag);
+	}
 }
 
 static void flush_qp(struct c4iw_qp *qhp)
 {
 	struct c4iw_cq *rchp, *schp;
+	unsigned long flag;
 
 	rchp = get_chp(qhp->rhp, qhp->attr.rcq);
 	schp = get_chp(qhp->rhp, qhp->attr.scq);
 
 	if (qhp->ibqp.uobject) {
 		t4_set_wq_in_error(&qhp->wq);
 		t4_set_cq_in_error(&rchp->cq);
+		spin_lock_irqsave(&rchp->comp_handler_lock, flag);
 		(*rchp->ibcq.comp_handler)(&rchp->ibcq, rchp->ibcq.cq_context);
+		spin_unlock_irqrestore(&rchp->comp_handler_lock, flag);
 		if (schp != rchp) {
 			t4_set_cq_in_error(&schp->cq);
+			spin_lock_irqsave(&schp->comp_handler_lock, flag);
 			(*schp->ibcq.comp_handler)(&schp->ibcq,
 					schp->ibcq.cq_context);
+			spin_unlock_irqrestore(&schp->comp_handler_lock, flag);
 		}
 		return;
 	}