IB/ehca: Check idr_find() return value

The idr_find() function may fail when trying to get the QP that is
associated with a CQE, e.g. when a QP has been destroyed between the
generation of a CQE and the poll request for it.  In consequence, the
return value of idr_find() must be checked and the CQE must be
discarded when the QP cannot be found.
Signed-off-by: Alexander Schmidt <alexs@linux.vnet.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/ehca/ehca_reqs.c

@@ -680,8 +680,10 @@ repoll:
 
 	read_lock(&ehca_qp_idr_lock);
 	my_qp = idr_find(&ehca_qp_idr, cqe->qp_token);
-	wc->qp = &my_qp->ib_qp;
 	read_unlock(&ehca_qp_idr_lock);
+	if (!my_qp)
+		goto repoll;
+	wc->qp = &my_qp->ib_qp;
 
 	wc->byte_len = cqe->nr_bytes_transferred;
 	wc->pkey_index = cqe->pkey_index;