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Re: [libvirt] [PATCHv3 08/43] snapshot: avoid crash when deleting qemu snapshots



On 08/24/2011 12:34 PM, Eric Blake wrote:
On 08/24/2011 10:38 AM, Daniel P. Berrange wrote:
On Wed, Aug 24, 2011 at 09:22:25AM -0600, Eric Blake wrote:
This one's nasty. Ever since we fixed virHashForEach to prevent
nested hash iterations for safety reasons, virDomainSnapshotDelete
with VIR_DOMAIN_SNAPSHOT_DELETE_CHILDREN has been broken for qemu:
it deletes children, while leaving grandchildren intact but pointing
to a no-longer-present parent. But even before then, the code would
often appear to succeed to clean up grandchildren, but risked memory
corruption if you have a large and deep hierarchy of snapshots.

I also still saw errors in libvirtd logs

17:36:36.175: 4423: info : libvirt version: 0.9.4
17:36:36.175: 4423: error : virHashSearch:604 : Hash operation not
allowed during iteration
17:36:36.176: 4423: warning : virDomainSnapshotMarkDescendant:11309 :
snapshot hash table is inconsistent!

Ouch; I can reproduce. I guess I didn't test this one as thoroughly as I
had planned, and this is indeed a bug in my 'forEachDescendant'
iterator. I'll post an update once I figure out where I went wrong.

Found the problem - virDomainSnapshotFindByName is doing a full hash search instead of a simple lookup - and recursive searches are verboten. Fix that, and we still have a problem - if the current snapshot is in the set of snapshots being deleted, then the parent snapshot needs to become current again. I'll post a couple of patches shortly.

--
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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