[Qemu-devel] [Bug] virtio-blk: qemu will crash if hotplug virtio-blk device failed

[linzhecheng]

I found that hotplug virtio-blk device will lead to qemu crash.

Re-production steps:

1.       Run VM named vm001

2.       Create a virtio-blk.xml which contains wrong configurations:
<disk device="lun" rawio="yes" type="block">
  <driver cache="none" io="native" name="qemu" type="raw" />
  <source dev="/dev/mapper/11-dm" />
  <target bus="virtio" dev="vdx" />
</disk>

3.       Run command : virsh attach-device vm001 vm001

Libvirt will return err msg:

error: Failed to attach device from blk-scsi.xml

error: internal error: unable to execute QEMU command 'device_add': Please set 
scsi=off for virtio-blk devices in order to use virtio 1.0

it means hotplug virtio-blk device failed.

4.       Suspend or shutdown VM will leads to qemu crash



from gdb:


(gdb) bt
#0  object_get_class (address@hidden) at qom/object.c:750
#1  0x00007f9a72582e01 in virtio_vmstate_change (opaque=0x7f9a73d10960, 
running=0, state=<optimized out>) at 
/mnt/sdb/lzc/code/open/qemu/hw/virtio/virtio.c:2203
#2  0x00007f9a7261ef52 in vm_state_notify (address@hidden, address@hidden) at 
vl.c:1685
#3  0x00007f9a7252603a in do_vm_stop (state=RUN_STATE_PAUSED) at 
/mnt/sdb/lzc/code/open/qemu/cpus.c:941
#4  vm_stop (address@hidden) at /mnt/sdb/lzc/code/open/qemu/cpus.c:1807
#5  0x00007f9a7262eb1b in qmp_stop (address@hidden) at qmp.c:102
#6  0x00007f9a7262c70a in qmp_marshal_stop (args=<optimized out>, 
ret=<optimized out>, errp=0x7ffe63e255d8) at qmp-marshal.c:5854
#7  0x00007f9a72897e79 in do_qmp_dispatch (errp=0x7ffe63e255d0, 
request=0x7f9a76510120, cmds=0x7f9a72ee7980 <qmp_commands>) at 
qapi/qmp-dispatch.c:104
#8  qmp_dispatch (cmds=0x7f9a72ee7980 <qmp_commands>, address@hidden) at 
qapi/qmp-dispatch.c:131
#9  0x00007f9a725288d5 in handle_qmp_command (parser=<optimized out>, 
tokens=<optimized out>) at /mnt/sdb/lzc/code/open/qemu/monitor.c:3852
#10 0x00007f9a7289d514 in json_message_process_token (lexer=0x7f9a73ce4498, 
input=0x7f9a73cc6880, type=JSON_RCURLY, x=36, y=17) at 
qobject/json-streamer.c:105
#11 0x00007f9a728bb69b in json_lexer_feed_char (address@hidden, ch=125 '}', 
address@hidden) at qobject/json-lexer.c:323
#12 0x00007f9a728bb75e in json_lexer_feed (lexer=0x7f9a73ce4498, 
buffer=<optimized out>, size=<optimized out>) at qobject/json-lexer.c:373
#13 0x00007f9a7289d5d9 in json_message_parser_feed (parser=<optimized out>, 
buffer=<optimized out>, size=<optimized out>) at qobject/json-streamer.c:124
#14 0x00007f9a7252722e in monitor_qmp_read (opaque=<optimized out>, 
buf=<optimized out>, size=<optimized out>) at 
/mnt/sdb/lzc/code/open/qemu/monitor.c:3894
#15 0x00007f9a7284ee1b in tcp_chr_read (chan=<optimized out>, cond=<optimized 
out>, opaque=<optimized out>) at chardev/char-socket.c:441
#16 0x00007f9a6e03e99a in g_main_context_dispatch () from 
/usr/lib64/libglib-2.0.so.0
#17 0x00007f9a728a342c in glib_pollfds_poll () at util/main-loop.c:214
#18 os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:261
#19 main_loop_wait (address@hidden) at util/main-loop.c:515
#20 0x00007f9a724e7547 in main_loop () at vl.c:1999
#21 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at 
vl.c:4877

Problem happens in virtio_vmstate_change which is called by vm_state_notify,
static void virtio_vmstate_change(void *opaque, int running, RunState state)
{
    VirtIODevice *vdev = opaque;
    BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
    bool backend_run = running && (vdev->status & VIRTIO_CONFIG_S_DRIVER_OK);
    vdev->vm_running = running;

    if (backend_run) {
        virtio_set_status(vdev, vdev->status);
    }

    if (k->vmstate_change) {
        k->vmstate_change(qbus->parent, backend_run);
    }

    if (!backend_run) {
        virtio_set_status(vdev, vdev->status);
    }
}

Vdev's parent_bus is NULL, so qdev_get_parent_bus(DEVICE(vdev)) will crash.
virtio_vmstate_change is added to the list vm_change_state_head at 
virtio_blk_device_realize(virtio_init),
but after hotplug virtio-blk failed, virtio_vmstate_change will not be removed 
from vm_change_state_head.


I apply a patch as follews:

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 5884ce3..ea532dc 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2491,6 +2491,7 @@ static void virtio_device_realize(DeviceState *dev, Error 
**errp)
     virtio_bus_device_plugged(vdev, &err);
     if (err != NULL) {
         error_propagate(errp, err);
+        vdc->unrealize(dev, NULL);
         return;
     }