File device_core-use-drain_call_rcu-in-in-qmp.patch of Package qemu.23275

From: Maxim Levitsky <mlevitsk@redhat.com>
Date: Tue, 6 Oct 2020 14:38:58 +0200
Subject: device_core: use drain_call_rcu in in qmp_device_add

Git-commit: 7bed89958bfbf40df9ca681cefbdca63abdde39d
References: bsc#1184574

Soon, a device removal might only happen on RCU callback execution.
This is okay for device-del which provides a DEVICE_DELETED event,
but not for the failure case of device-add.  To avoid changing
monitor semantics, just drain all pending RCU callbacks on error.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Suggested-by: Stefan Hajnoczi <stefanha@gmail.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20200913160259.32145-4-mlevitsk@redhat.com>
[Don't use it in qmp_device_del. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Lin Ma <lma@suse.com>
---
 qdev-monitor.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/qdev-monitor.c b/qdev-monitor.c
index dc0323051e33833c4bcb638c7657..ade59c9ec6a54a258cc5ab21ace4 100644
--- a/qdev-monitor.c
+++ b/qdev-monitor.c
@@ -796,6 +796,18 @@ void qmp_device_add(QDict *qdict, QObject **ret_data, Error **errp)
         return;
     }
     dev = qdev_device_add(opts, &local_err);
+
+    /*
+     * Drain all pending RCU callbacks. This is done because
+     * some bus related operations can delay a device removal
+     * (in this case this can happen if device is added and then
+     * removed due to a configuration error)
+     * to a RCU callback, but user might expect that this interface
+     * will finish its job completely once qmp command returns result
+     * to the user
+     */
+    drain_call_rcu();
+
     if (!dev) {
         error_propagate(errp, local_err);
         qemu_opts_del(opts);