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virtio-scsi: fix hotplug ->reset() vs event race 

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>
This commit is contained in:
Stefan Hajnoczi 2018-07-16 09:37:32 +01:00 committed by Paolo Bonzini
parent 25e8978817
commit 8449bcf949
1 changed files with 10 additions and 1 deletions
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11
hw/scsi/virtio-scsi.c
View File

@ -797,8 +797,16 @@ 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);
@ -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;
}