[Xen-bugs] [Bug 1411] New: (User created) Race between XEN and LVM leaves open logical volumes

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1411

           Summary: (User created) Race between XEN and LVM leaves open
                    logical volumes
           Product: Xen
           Version: unspecified
          Platform: x86-64
        OS/Version: Linux-2.6
            Status: NEW
          Severity: normal
          Priority: P3
         Component: Tools
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: pehrs@xxxxxx


I am running XEN (3.3.1_18494_03-1.8) on an OpenSUSE 11.1 system
(2.6.27.7-9-xen). I am using a storage based on LVM2 snapshots for the XEN
instances. Regularly I want to remove all the systems and create fresh systems
using snapshots. 

If I have 20 instances running and execute a simple script that does:

xm shutdown <20 instances>
and then directly
lvremove -f <20 related snapshots>

Something strange will happen in LVM. I get an error of the type: 

â??Can't remove open logical volumeâ??

for 2-4 of the snapshots that are left with an open reference. This makes
sense, as XEN might not have completed shutting down. However, this open
reference remains after xen completes shutdown and the instances are no longer
visible in xm list. The reference does not show up anywhere but in the
lvdisplay where the open counter is â??1â??. Fuser and similar commands does
not show it. 

This makes it impossible to remove the snapshot. To remove the open reference I
have to reboot the server or to recreate the xen instance and then shut it down
again.

Simply waiting a bit between the two commands, so the virtual instances
completes shutdown, is enough to prevent this from happening. I suspect that
trying to destroy the snapshot during the shutdown sequence somehow leaves the
open reference.

Trying to destroy the storage of a running system is never a good idea, but i
don't think it's good that  the volume is left open after the instance that was
using it is shut down.


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