IB/core: Use qp->usecnt to track multicast attach/detach

Just as we don't allow PDs, CQs, etc. to be destroyed if there are QPs
that are attached to them, don't let a QP be destroyed if there are
multicast group(s) attached to it. Use the existing usecnt field of
struct ib_qp which was added by commit 0e0ec7e ("RDMA/core: Export
ib_open_qp() to share XRC TGT QPs") to track this.

Signed-off-by: Or Gerlitz <[e-mail]>
Signed-off-by: Roland Dreier <[e-mail]>

drivers/infiniband/core/verbs.c

···
 
 int ib_attach_mcast(struct ib_qp *qp, union ib_gid *gid, u16 lid)
 {
+	int ret;
+
 	if (!qp->device->attach_mcast)
 		return -ENOSYS;
 	if (gid->raw[0] != 0xff || qp->qp_type != IB_QPT_UD)
 		return -EINVAL;
 
-	return qp->device->attach_mcast(qp, gid, lid);
+	ret = qp->device->attach_mcast(qp, gid, lid);
+	if (!ret)
+		atomic_inc(&qp->usecnt);
+	return ret;
 }
 EXPORT_SYMBOL(ib_attach_mcast);
 
 int ib_detach_mcast(struct ib_qp *qp, union ib_gid *gid, u16 lid)
 {
+	int ret;
+
 	if (!qp->device->detach_mcast)
 		return -ENOSYS;
 	if (gid->raw[0] != 0xff || qp->qp_type != IB_QPT_UD)
 		return -EINVAL;
 
-	return qp->device->detach_mcast(qp, gid, lid);
+	ret = qp->device->detach_mcast(qp, gid, lid);
+	if (!ret)
+		atomic_dec(&qp->usecnt);
+	return ret;
 }
 EXPORT_SYMBOL(ib_detach_mcast);
 

include/rdma/ib_verbs.h

···
 	struct ib_srq	       *srq;
 	struct ib_xrcd	       *xrcd; /* XRC TGT QPs only */
 	struct list_head	xrcd_list;
-	atomic_t		usecnt; /* count times opened */
+	atomic_t		usecnt; /* count times opened, mcast attaches */
 	struct list_head	open_list;
 	struct ib_qp           *real_qp;
 	struct ib_uobject      *uobject;