Description Philipp Hahn 2014-07-31 09:22:56 CEST

+++ This bug was initially created as a clone of Bug #20481 +++
This happened twice again with UCS-3.2-2, which has the patch from Bug #20481 applied:

# cat /var/log/daemon.log
Jul 31 08:35:58 lynx1 logger: /etc/xen/scripts/block: add XENBUS_PATH=backend/vbd/1/768
Jul 31 08:35:58 lynx1 logger: /etc/xen/scripts/block: Path still initializing: backend/vbd/1/768
...
Jul 31 08:37:38 lynx1 logger: /etc/xen/scripts/block: Path still initializing: backend/vbd/1/768
Jul 31 08:37:39 lynx1 logger: /etc/xen/scripts/block: Writing backend/vbd/1/768/hotplug-error Path closed or removed during hotplug add: backend/vbd/1/768 state: 5 backend/vbd/1/768/hotplug-status error to xenstore.
Jul 31 08:37:39 lynx1 logger: /etc/xen/scripts/block: Path closed or removed during hotplug add: backend/vbd/1/768 state: 5

Trying to start the VM a second time works with the following messages:
Jul 31 08:43:02 lynx1 logger: /etc/xen/scripts/block: add XENBUS_PATH=backend/vbd/2/768
Jul 31 08:43:02 lynx1 logger: /etc/xen/scripts/block: Writing backend/vbd/2/768/node /dev/loop0 to xenstore.
Jul 31 08:43:02 lynx1 logger: /etc/xen/scripts/block: Writing backend/vbd/2/768/physical-device 7:0 to xenstore.
Jul 31 08:43:02 lynx1 logger: /etc/xen/scripts/block: Writing backend/vbd/2/768/hotplug-status connected to xenstore.


So for some unknown reason xen_blkbk_probe() from drivers/block/xen-blkback/xenbus.c:448 doesn't seem to be called.

The module "xen_blkback" was the last module, which was loaded:
# head -n 1 /proc/modules
xen_blkback 21814 0 [permanent], Live 0xffffffffa05af000

dom0 kernel log has this:
# dmesg
[53251.794640] vbd vbd-1-768: 2 unable to read other end from backend/vbd/1/768.  missing or inaccessible.
[53251.799923] vbd vbd-1-768: talk_to_otherend on backend/vbd/1/768 failed.
[53251.799928] vbd: probe of vbd-1-768 failed with error -2

Those messages are from drivers/xen/xenbus/xenbus_probe.c
209 int xenbus_dev_probe(struct device *_dev)
...
229 »···err = talk_to_otherend(dev);                                                                                
230 »···if (err) {
231 »···»···dev_warn(&dev->dev, "talk_to_otherend on %s failed.\n",
232 »···»···»··· dev->nodename);

119 static int talk_to_otherend(struct xenbus_device *dev)                                                          
...
126 »···return drv->read_otherend_details(dev);

142 int xenbus_read_otherend_details(struct xenbus_device *xendev,
...
157 »···»···xenbus_dev_fatal(xendev, -ENOENT,
158 »···»···»···»··· "unable to read other end from %s.  "
159 »···»···»···»··· "missing or inaccessible.",
160 »···»···»···»··· xendev->nodename);