Revert "irqbypass: do not start cons/prod when failed connect"

This reverts commit a979a6aa.

The reverted commit may cause VM freeze on arm64 with GICv4,
where stopping a consumer is implemented by suspending the VM.
Should the connect fail, the VM will not be resumed, which
is a bit of a problem.

It also erroneously calls the producer destructor unconditionally,
which is unexpected.
Reported-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Suggested-by: Marc Zyngier <maz@kernel.org>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Shaokun Zhang <zhangshaokun@hisilicon.com>
Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
[maz: tags and cc-stable, commit message update]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Fixes: a979a6aa ("irqbypass: do not start cons/prod when failed connect")
Link: https://lore.kernel.org/r/3a2c66d6-6ca0-8478-d24b-61e8e3241b20@hisilicon.com
Link: https://lore.kernel.org/r/20210508071152.722425-1-lingshan.zhu@intel.com
Cc: stable@vger.kernel.org

virt/lib/irqbypass.c

@@ -40,21 +40,17 @@ static int __connect(struct irq_bypass_producer *prod,
 	if (prod->add_consumer)
 		ret = prod->add_consumer(prod, cons);
 
-	if (ret)
-		goto err_add_consumer;
-
-	ret = cons->add_producer(cons, prod);
-	if (ret)
-		goto err_add_producer;
+	if (!ret) {
+		ret = cons->add_producer(cons, prod);
+		if (ret && prod->del_consumer)
+			prod->del_consumer(prod, cons);
+	}
 
 	if (cons->start)
 		cons->start(cons);
 	if (prod->start)
 		prod->start(prod);
-err_add_producer:
-	if (prod->del_consumer)
-		prod->del_consumer(prod, cons);
-err_add_consumer:
+
 	return ret;
 }