From b872baa52f5e8e8c84b3a19bb6cf5b6e92106fb9 Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Tue, 24 Jul 2018 15:13:08 +0200
Subject: [PATCH 264/268] virtio-scsi: fix hotplug ->reset() vs event race

RH-Author: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: <20180724151308.20500-3-stefanha@redhat.com>
Patchwork-id: 81486
O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 2/2] virtio-scsi: fix hotplug ->reset() vs event race
Bugzilla: 1607891
RH-Acked-by: Igor Mammedov <imammedo@redhat.com>
RH-Acked-by: Pankaj Gupta <pagupta@redhat.com>
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>

There is a race condition during hotplug when iothread is used.  It
occurs because virtio-scsi may be processing command queues in the
iothread while the monitor performs SCSI device hotplug.

When a SCSI device is hotplugged the HotplugHandler->plug() callback is
invoked and virtio-scsi emits a rescan event to the guest.

If the guest submits a SCSI command at this point then it may be
cancelled before hotplug completes.  This happens because ->reset() is
called by hw/core/qdev.c:device_set_realized() after
HotplugHandler->plug() has been called and
hw/scsi/scsi-disk.c:scsi_disk_reset() purges all requests.

This patch uses the new HotplugHandler->post_plug() callback to emit the
rescan event after ->reset().  This eliminates the race conditions where
requests could be cancelled.

Reported-by: l00284672 <lizhengui@huawei.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20180716083732.3347-3-stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 8449bcf94986156a1476d6647c75ec1ce3db64d0)
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 hw/scsi/virtio-scsi.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 9f754c4..52a3c1d 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -806,8 +806,16 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
         virtio_scsi_acquire(s);
         blk_set_aio_context(sd->conf.blk, s->ctx);
         virtio_scsi_release(s);
-
     }
+}
+
+/* Announce the new device after it has been plugged */
+static void virtio_scsi_post_hotplug(HotplugHandler *hotplug_dev,
+                                     DeviceState *dev)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(hotplug_dev);
+    VirtIOSCSI *s = VIRTIO_SCSI(vdev);
+    SCSIDevice *sd = SCSI_DEVICE(dev);
 
     if (virtio_vdev_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG)) {
         virtio_scsi_acquire(s);
@@ -977,6 +985,7 @@ static void virtio_scsi_class_init(ObjectClass *klass, void *data)
     vdc->start_ioeventfd = virtio_scsi_dataplane_start;
     vdc->stop_ioeventfd = virtio_scsi_dataplane_stop;
     hc->plug = virtio_scsi_hotplug;
+    hc->post_plug = virtio_scsi_post_hotplug;
     hc->unplug = virtio_scsi_hotunplug;
 }
 
-- 
1.8.3.1