Re: [libvirt] [PATCH 1/2] qemu: Add missing lock of virDomainObj before calling virDomainUnref

On 03/04/2011 02:46 PM, Eric Blake wrote: I think the real reason for the deadlock is that: qemudDomainSaveFlag holds the domain lock while it calls qemuDomainEventQueue, which requests the event loop lock the event loop thread holds the event loop lock, and can make several different callbacks that can result in requesting a domain lock I counted 29 callers of qemuDomainEventQueue; the majority of those were in situations where the domain lock had already been dropped (in fact, it makes sense to generate the event while you own the domain, but wait to fire it off until after you are done with the domain). But these culprits either held a domain lock, or I couldn't quickly see if they might hold a domain lock higher in the call stack: qemuMigrationSetOffline in qemu_migration.c has the domain lock qemudDomainSaveFlag in qemu_driver.c qemuDomainRevertToSnapshot in qemu_driver.c Not sure about: qemuMigrationFinish in qemu_migration.c qemudNotifyLoadDomain in qemu_driver.c qemudDomainSaveImageStart in qemu_driver.c qemuDomainObjStart in qemu_driver.c Of those, qemuDomainRevertToSnapshot can easily be fixed by swapping the unlock and event queue calls. But the rest could probably use a helper method that increases the vm ref count, unlocks the domain lock, fires the event, grabs the domain lock, reduces the vm ref count, and checks that the domain is still active. However, I ran out of time to code that up for now, and am not positive that it is the right solution. Dan, your thoughts? -- Eric Blake eblake(a)redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org