On Thu, Feb 28, 2013 at 01:33:31PM +0000, Daniel P. Berrange wrote: > From: "Daniel P. Berrange" <berrange@xxxxxxxxxx> > > There is a lock ordering problem in the QEMU close callback > APIs. > > When starting a guest we have a lock on the VM. We then > set a autodestroy callback, which acquires a lock on the > close callbacks. > > When running auto-destroy, we obtain a lock on the close > callbacks, then run each callbacks - which obtains a lock > on the VM. > > This causes deadlock if anyone tries to start a VM, while > autodestroy is taking place. > > The fix is to do autodestroy in 2 phases. First obtain > all the callbacks and remove them from the list under > the close callback lock. Then invoke each callback > from outside the close callback lock. > > Signed-off-by: Daniel P. Berrange <berrange@xxxxxxxxxx> > --- > src/qemu/qemu_conf.c | 106 ++++++++++++++++++++++++++++++++++++++++++-------- > src/util/virnetlink.c | 5 ++- > 2 files changed, 92 insertions(+), 19 deletions(-) Incidentally this patch is also a huge performance win. Previously once autodestroy starts running it blocks all startup/shutdown of VMs. When a single client had created 1000 VMs, this blocked libvirtd for a very long time indeed. With this change we get full parallelism in auto-destroy since only 1 VM at a time is locked, and other VMs can continue to start/stop Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list