Re: [libvirt] [PATCH v2 2/2] qemu: avoid rare race when undefining domain

When one domain is being undefined and at the same time started, for example, there is a possibility of a rare problem occuring. - Thread 1 does virDomainUndefine(), has the lock, checks that the domain is active and because it's not, calls virDomainObjListRemove(). - Thread 2 does virDomainCreate() and tries to lock the domain. - Thread 1 needs to lock domain list in order to remove the domain from it, but must unlock domain first (proper order is to lock domain list first and the domain itself second). - Thread 2 grabs the lock, starts the domain and releases the lock. - Thread 1 grabs the lock and removes the domain from list. With this patch: - qemuDomainRemoveInactive() creates a QEMU_JOB_MODIFY if that's possible, but since it must remove the domain from list either way, it continues even when starting the job failed. - Because virDomainObjListRemove() removes a reference to the virDomainObj (and it must be kept that way for other drivers), we hack around that by acquiring one more reference that's kept until the job is ended. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1150505 Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com&gt; --- src/qemu/qemu_domain.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c index 76fccce..98c4763 100644 --- a/src/qemu/qemu_domain.c +++ b/src/qemu/qemu_domain.c @@ -2392,9 +2392,13 @@ void qemuDomainRemoveInactive(virQEMUDriverPtr driver, virDomainObjPtr vm) { + bool haveJob = true; char *snapDir; virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver); + if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0) + haveJob = false; + /* Remove any snapshot metadata prior to removing the domain */ if (qemuDomainSnapshotDiscardAllMetadata(driver, vm) < 0) { VIR_WARN("unable to remove all snapshots for domain %s", @@ -2409,8 +2413,13 @@ qemuDomainRemoveInactive(virQEMUDriverPtr driver, VIR_WARN("unable to remove snapshot directory %s", snapDir); VIR_FREE(snapDir); } + virObjectRef(vm); virDomainObjListRemove(driver->domains, vm); virObjectUnref(cfg); + + if (haveJob) + ignore_value(qemuDomainObjEndJob(driver, vm)); + virObjectUnref(vm); } void