Re: [libvirt PATCH 2/5] nwfilter: hold filter update lock when creating/deleting bindings

The nwfilter update lock is historically acquired by the virt drivers in order to achieve serialization between nwfilter define/undefine, and instantiation/teardown of filters. When running in the modular daemons, however, the mutex that the virt drivers are locking is in a completely different process from the mutex that the nwfilter driver is locking. Serialization is lost and thus call from the virt driver to virNWFilterBindingCreateXML can deadlock with a concurrent call to the virNWFilterDefineXML method. The solution is surprisingly easy, the update lock simply needs acquiring in the virNWFilterBindingCreateXML method and virNWFilterBindingUndefine method instead of in the virt drivers. The only semantic difference here is that when a virtual machine has multiple NICs, the instantiation and teardown of filters is no longer serialized for the whole VM, but rather for each NIC. This should not be a problem since the virt drivers already need to cope with tearing down a partially created VM where only some of the NICs are setup. Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt;

--- src/nwfilter/nwfilter_driver.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/src/nwfilter/nwfilter_driver.c b/src/nwfilter/nwfilter_driver.c index 08f138dd79..3ce8fce7f9 100644 --- a/src/nwfilter/nwfilter_driver.c +++ b/src/nwfilter/nwfilter_driver.c @@ -760,11 +760,14 @@ nwfilterBindingCreateXML(virConnectPtr conn, if (!(ret = virGetNWFilterBinding(conn, def->portdevname, def->filter))) goto cleanup; + virNWFilterReadLockFilterUpdates(); if (virNWFilterInstantiateFilter(driver, def) < 0) { + virNWFilterUnlockFilterUpdates(); virNWFilterBindingObjListRemove(driver->bindings, obj); g_clear_pointer(&ret, virObjectUnref); goto cleanup; } + virNWFilterUnlockFilterUpdates(); virNWFilterBindingObjSave(obj, driver->bindingDir); cleanup: @@ -801,7 +804,9 @@ nwfilterBindingDelete(virNWFilterBindingPtr binding) if (virNWFilterBindingDeleteEnsureACL(binding->conn, def) < 0) goto cleanup; + virNWFilterReadLockFilterUpdates(); virNWFilterTeardownFilter(def); + virNWFilterUnlockFilterUpdates(); virNWFilterBindingObjDelete(obj, driver->bindingDir); virNWFilterBindingObjListRemove(driver->bindings, obj);