IB/core: Protect against self-requeue of a cq work item

We need to make sure that the cq work item does not
run when we are destroying the cq. Unlike flush_work,
cancel_work_sync protects against self-requeue of the
work item (which we can do in ib_cq_poll_work).
Signed-off-by: NSagi Grimberg <sagi@grimberg.me>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>--
Reviewed-by: NLeon Romanovsky <leonro@mellanox.com>
Signed-off-by: NDoug Ledford <dledford@redhat.com>

drivers/infiniband/core/cq.c

@@ -196,7 +196,7 @@ void ib_free_cq(struct ib_cq *cq)
 		irq_poll_disable(&cq->iop);
 		break;
 	case IB_POLL_WORKQUEUE:
-		flush_work(&cq->work);
+		cancel_work_sync(&cq->work);
 		break;
 	default:
 		WARN_ON_ONCE(1);