Re: [libvirt] [PATCH] qemu: Resolve agent deadlock

If we have a shutdown of a VM by a qemu agent while an agent EOF occurs at relatively the same time, it's possible that a deadlock occurs depending on what happens first. Assume qemuProcessHandleAgentEOF runs first, with the vm->lock it clears priv->agent, then clears the vm->lock.

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c index 890d8ed..a908df8 100644 --- a/src/qemu/qemu_domain.c +++ b/src/qemu/qemu_domain.c @@ -1868,19 +1868,20 @@ qemuDomainObjEnterAgent(virDomainObjPtr obj) * Should be paired with an earlier qemuDomainObjEnterAgent() call */ void -qemuDomainObjExitAgent(virDomainObjPtr obj) +qemuDomainObjExitAgent(virDomainObjPtr obj, + qemuAgentPtr agent)

{ qemuDomainObjPrivatePtr priv = obj->privateData; bool hasRefs; - hasRefs = virObjectUnref(priv->agent); + hasRefs = virObjectUnref(agent); if (hasRefs) - virObjectUnlock(priv->agent); + virObjectUnlock(agent); virObjectLock(obj); - VIR_DEBUG("Exited agent (agent=%p vm=%p name=%s)", - priv->agent, obj, obj->def->name); + VIR_DEBUG("Exited agent (agent=%p vm=%p name=%s hasRefs=%d)", + agent, obj, obj->def->name, hasRefs); priv->agentStart = 0; if (!hasRefs)

void qemuDomainObjEnterRemote(virDomainObjPtr obj) diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index a2cc002..b8c9ff7 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -1994,9 +1994,10 @@ static int qemuDomainShutdownFlags(virDomainPtr dom, unsigned int flags) qemuDomainSetFakeReboot(driver, vm, isReboot); if (useAgent) { + qemuAgentPtr agent = priv->agent; qemuDomainObjEnterAgent(vm); - ret = qemuAgentShutdown(priv->agent, agentFlag); - qemuDomainObjExitAgent(vm); + ret = qemuAgentShutdown(agent, agentFlag); + qemuDomainObjExitAgent(vm, agent);