Re: [libvirt] [PATCH] Fix potential events deadlock when unref'ing virConnectPtr

From: "Daniel P. Berrange" <berrange(a)redhat.com&gt; When the last reference to a virConnectPtr is released by libvirtd, it was possible for a deadlock to occur in the virDomainEventState functions. The virDomainEventStatePtr holds a reference on virConnectPtr for each registered callback. When removing a callback, the virUnrefConnect function is run. If this causes the last reference on the virConnectPtr to be released, then virReleaseConnect can be run, which in turns calls qemudClose. This function has a call to virDomainEventStateDeregisterConn which is intended to remove all callbacks associated with the virConnectPtr instance. Since each callback associated with a virConnectPtr holds a reference on virConnectPtr, it is impossible for the qemudClose method to be invoked while any callbacks are still registered. Thus the call to virDomainEventStateDeregisterConn must in fact be a no-op. Thus it is possible to just remove all trace of virDomainEventStateDeregisterConn and avoid the deadlock. * src/conf/domain_event.c, src/conf/domain_event.h, src/libvirt_private.syms: Delete virDomainEventStateDeregisterConn * src/libxl/libxl_driver.c, src/lxc/lxc_driver.c, src/qemu/qemu_driver.c, src/uml/uml_driver.c: Remove calls to virDomainEventStateDeregisterConn --- src/conf/domain_event.c | 61 ---------------------------------------------- src/conf/domain_event.h | 4 --- src/libvirt_private.syms | 1 - src/libxl/libxl_driver.c | 4 --- src/lxc/lxc_driver.c | 2 -- src/qemu/qemu_driver.c | 2 -- src/uml/uml_driver.c | 2 -- 7 files changed, 76 deletions(-)