[2/2] virtio-scsi: fix hotplug ->reset() vs event race

Message ID 20180710155037.16834-3-stefanha@redhat.com
State New
Headers show
  • virtio-scsi: fix hotplug ->reset() vs event race
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Commit Message

Stefan Hajnoczi July 10, 2018, 3:50 p.m.
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>
 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 3aa99717e2..1ec808e6fd 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -797,8 +797,16 @@  static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
         blk_set_aio_context(sd->conf.blk, s->ctx);
+/* Announce the new device after it has been plugged */
+static void virtio_scsi_post_hotplug(HotplugHandler *hotplug_dev,
+                                     DeviceState *dev, Error **errp)
+    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)) {
@@ -968,6 +976,7 @@  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;