qemu_hotplug: delay sending DEVICE_REMOVED event until after *all* teardown

The VIR_DOMAIN_EVENT_ID_DEVICE_REMOVED event is sent after qemu has
responded to a device_del command with a DEVICE_DELETED event. Before
queuing the event, *some* of the final teardown of the device's
trappings in libvirt is done, but not *all* of it. As a result, an
application may receive and process the DEVICE_REMOVED event before
libvirt has really finished with it.

Usually this doesn't cause a problem, but it can - in the case of the
bug report referenced below, vdsm is assigning a PCI device to a guest
with managed='no', using livirt's virNodeDeviceDetachFlags() and
virNodeDeviceReAttach() APIs. Immediately after receiving a
DEVICE_REMOVED event from libvirt signalling that the device had been
successfully unplugged, vdsm would cal virNodeDeviceReAttach() to
unbind the device from vfio-pci and rebind it to the host driverm but
because the event was received before libvirt had completely finished
processing the removal, that device was still on the "activeDevs"
list, and so virNodeDeviceReAttach() failed.

Experimentation with additional debug logs proved that libvirt would
always end up dispatching the DEVICE_REMOVED event before it had
removed the device from activeDevs (with a *much* greater difference
with managed='yes', since in that case the re-binding of the device
occurred after queuing the device).

Although the case of hostdev devices is the most extreme (since there
is so much involved in tearing down the device), *all* device types
suffer from the same problem - the DEVICE_REMOVED event is queued very
early in the qemuDomainRemove*Device() function for all of them,
resulting in a possibility of any application receiving the event
before libvirt has really finished with the device.

The solution is to save the device's alias (which is the only piece of
info from the device object that is needed for the event) at the
beginning of processing the device removal, and then queue the event
as a final act before returning. Since all of the
qemuDomainRemove*Device() functions (except
qemuDomainRemoveChrDevice()) are now called exclusively from
qemuDomainRemoveDevice() (which selects which of the subordinates to
call in a switch statement based on the type of device), the shortest
route to a solution is to doing the saving of alias, and later
queueing of the event, in the higher level qemuDomainRemoveDevice(),
and just completely remove the event-related code from all the
subordinate functions.

The single exception to this, as mentioned before, is
qemuDomainRemoveChrDevice(), which is still called from somewhere
other than qemuDomainRemoveDevice() (and has a separate arg used to
trigger different behavior when the chr device has targetType ==
GUESTFWD), so it must keep its original behavior intact, and must be
treated differently by qemuDomainRemoveDevice() (similar to the way
that qemuDomainDetachDeviceLive() treats chr and lease devices
differently from all the others).

Resolves: https://bugzilla.redhat.com/1658198Signed-off-by: NLaine Stump <laine@laine.org>
ACKed-by: NPeter Krempa <pkrempa@redhat.com>

src/qemu/qemu_hotplug.c

@@ -4481,7 +4481,6 @@ qemuDomainRemoveDiskDevice(virQEMUDriverPtr driver,
 {
     qemuHotplugDiskSourceDataPtr diskbackend = NULL;
     virDomainDeviceDef dev;
-    virObjectEventPtr event;
     size_t i;
     qemuDomainObjPrivatePtr priv = vm->privateData;
     int ret = -1;
@@ -4509,9 +4508,6 @@ qemuDomainRemoveDiskDevice(virQEMUDriverPtr driver,
 
     virDomainAuditDisk(vm, disk->src, NULL, "detach", true);
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, disk->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     qemuDomainReleaseDeviceAddress(vm, &disk->info, virDomainDiskGetSource(disk));
 
     /* tear down disk security access */
@@ -4535,19 +4531,14 @@ qemuDomainRemoveDiskDevice(virQEMUDriverPtr driver,
 
 
 static int
-qemuDomainRemoveControllerDevice(virQEMUDriverPtr driver,
-                                 virDomainObjPtr vm,
+qemuDomainRemoveControllerDevice(virDomainObjPtr vm,
                                  virDomainControllerDefPtr controller)
 {
-    virObjectEventPtr event;
     size_t i;
 
     VIR_DEBUG("Removing controller %s from domain %p %s",
               controller->info.alias, vm, vm->def->name);
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, controller->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     for (i = 0; i < vm->def->ncontrollers; i++) {
         if (vm->def->controllers[i] == controller) {
             virDomainControllerRemove(vm->def, i);
@@ -4569,7 +4560,6 @@ qemuDomainRemoveMemoryDevice(virQEMUDriverPtr driver,
     qemuDomainObjPrivatePtr priv = vm->privateData;
     unsigned long long oldmem = virDomainDefGetMemoryTotal(vm->def);
     unsigned long long newmem = oldmem - mem->size;
-    virObjectEventPtr event;
     char *backendAlias = NULL;
     int rc;
     int idx;
@@ -4591,9 +4581,6 @@ qemuDomainRemoveMemoryDevice(virQEMUDriverPtr driver,
     if (rc < 0)
         return -1;
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, mem->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     if ((idx = virDomainMemoryFindByDef(vm->def, mem)) >= 0)
         virDomainMemoryRemove(vm->def, idx);
 
@@ -4673,7 +4660,6 @@ qemuDomainRemoveHostDevice(virQEMUDriverPtr driver,
 {
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     virDomainNetDefPtr net = NULL;
-    virObjectEventPtr event;
     size_t i;
     int ret = -1;
     qemuDomainObjPrivatePtr priv = vm->privateData;
@@ -4717,9 +4703,6 @@ qemuDomainRemoveHostDevice(virQEMUDriverPtr driver,
             goto cleanup;
     }
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, hostdev->info->alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     if (hostdev->parent.type == VIR_DOMAIN_DEVICE_NET) {
         net = hostdev->parent.data.net;
 
@@ -4798,7 +4781,6 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
 {
     virQEMUDriverConfigPtr cfg = virQEMUDriverGetConfig(driver);
     qemuDomainObjPrivatePtr priv = vm->privateData;
-    virObjectEventPtr event;
     char *hostnet_name = NULL;
     char *charDevAlias = NULL;
     size_t i;
@@ -4843,9 +4825,6 @@ qemuDomainRemoveNetDevice(virQEMUDriverPtr driver,
 
     virDomainAuditNet(vm, net, NULL, "detach", true);
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, net->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     for (i = 0; i < vm->def->nnets; i++) {
         if (vm->def->nets[i] == net) {
             virDomainNetRemove(vm->def, i);
@@ -4928,11 +4907,16 @@ qemuDomainRemoveChrDevice(virQEMUDriverPtr driver,
     if (qemuDomainNamespaceTeardownChardev(vm, chr) < 0)
         VIR_WARN("Unable to remove chr device from /dev");
 
+    qemuDomainReleaseDeviceAddress(vm, &chr->info, NULL);
+    qemuDomainChrRemove(vm->def, chr);
+
+    /* The caller does not emit the event, so we must do it here. Note
+     * that the event should be reported only after all backend
+     * teardown is completed.
+     */
     event = virDomainEventDeviceRemovedNewFromObj(vm, chr->info.alias);
     virObjectEventStateQueue(driver->domainEventState, event);
 
-    qemuDomainReleaseDeviceAddress(vm, &chr->info, NULL);
-    qemuDomainChrRemove(vm->def, chr);
     virDomainChrDefFree(chr);
     ret = 0;
 
@@ -4947,7 +4931,6 @@ qemuDomainRemoveRNGDevice(virQEMUDriverPtr driver,
                           virDomainObjPtr vm,
                           virDomainRNGDefPtr rng)
 {
-    virObjectEventPtr event;
     char *charAlias = NULL;
     char *objAlias = NULL;
     qemuDomainObjPrivatePtr priv = vm->privateData;
@@ -4996,9 +4979,6 @@ qemuDomainRemoveRNGDevice(virQEMUDriverPtr driver,
     if (qemuDomainNamespaceTeardownRNG(vm, rng) < 0)
         VIR_WARN("Unable to remove RNG device from /dev");
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, rng->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     if ((idx = virDomainRNGFind(vm->def, rng)) >= 0)
         virDomainRNGRemove(vm->def, idx);
     qemuDomainReleaseDeviceAddress(vm, &rng->info, NULL);
@@ -5023,7 +5003,6 @@ qemuDomainRemoveShmemDevice(virQEMUDriverPtr driver,
     char *charAlias = NULL;
     char *memAlias = NULL;
     qemuDomainObjPrivatePtr priv = vm->privateData;
-    virObjectEventPtr event = NULL;
 
     VIR_DEBUG("Removing shmem device %s from domain %p %s",
               shmem->info.alias, vm, vm->def->name);
@@ -5051,9 +5030,6 @@ qemuDomainRemoveShmemDevice(virQEMUDriverPtr driver,
     if (rc < 0)
         goto cleanup;
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, shmem->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     if ((idx = virDomainShmemDefFind(vm->def, shmem)) >= 0)
         virDomainShmemDefRemove(vm->def, idx);
     qemuDomainReleaseDeviceAddress(vm, &shmem->info, NULL);
@@ -5069,17 +5045,12 @@ qemuDomainRemoveShmemDevice(virQEMUDriverPtr driver,
 
 
 static int
-qemuDomainRemoveWatchdog(virQEMUDriverPtr driver,
-                         virDomainObjPtr vm,
+qemuDomainRemoveWatchdog(virDomainObjPtr vm,
                          virDomainWatchdogDefPtr watchdog)
 {
-    virObjectEventPtr event = NULL;
-
     VIR_DEBUG("Removing watchdog %s from domain %p %s",
               watchdog->info.alias, vm, vm->def->name);
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, watchdog->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
     qemuDomainReleaseDeviceAddress(vm, &watchdog->info, NULL);
     virDomainWatchdogDefFree(vm->def->watchdog);
     vm->def->watchdog = NULL;
@@ -5091,16 +5062,11 @@ static int
 qemuDomainRemoveInputDevice(virDomainObjPtr vm,
                             virDomainInputDefPtr dev)
 {
-    qemuDomainObjPrivatePtr priv = vm->privateData;
-    virQEMUDriverPtr driver = priv->driver;
-    virObjectEventPtr event = NULL;
     size_t i;
 
     VIR_DEBUG("Removing input device %s from domain %p %s",
               dev->info.alias, vm, vm->def->name);
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, dev->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
     for (i = 0; i < vm->def->ninputs; i++) {
         if (vm->def->inputs[i] == dev)
             break;
@@ -5125,15 +5091,9 @@ static int
 qemuDomainRemoveVsockDevice(virDomainObjPtr vm,
                             virDomainVsockDefPtr dev)
 {
-    qemuDomainObjPrivatePtr priv = vm->privateData;
-    virQEMUDriverPtr driver = priv->driver;
-    virObjectEventPtr event = NULL;
-
     VIR_DEBUG("Removing vsock device %s from domain %p %s",
               dev->info.alias, vm, vm->def->name);
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, dev->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
     qemuDomainReleaseDeviceAddress(vm, &dev->info, NULL);
     virDomainVsockDefFree(vm->def->vsock);
     vm->def->vsock = NULL;
@@ -5147,7 +5107,6 @@ qemuDomainRemoveRedirdevDevice(virQEMUDriverPtr driver,
                                virDomainRedirdevDefPtr dev)
 {
     qemuDomainObjPrivatePtr priv = vm->privateData;
-    virObjectEventPtr event;
     char *charAlias = NULL;
     ssize_t idx;
     int ret = -1;
@@ -5172,9 +5131,6 @@ qemuDomainRemoveRedirdevDevice(virQEMUDriverPtr driver,
 
     virDomainAuditRedirdev(vm, dev, "detach", true);
 
-    event = virDomainEventDeviceRemovedNewFromObj(vm, dev->info.alias);
-    virObjectEventStateQueue(driver->domainEventState, event);
-
     if ((idx = virDomainRedirdevDefFind(vm->def, dev)) >= 0)
         virDomainRedirdevDefRemove(vm->def, idx);
     qemuDomainReleaseDeviceAddress(vm, &dev->info, NULL);
@@ -5257,50 +5213,79 @@ qemuDomainRemoveDevice(virQEMUDriverPtr driver,
                        virDomainObjPtr vm,
                        virDomainDeviceDefPtr dev)
 {
-    int ret = -1;
+    virDomainDeviceInfoPtr info;
+    virObjectEventPtr event;
+    VIR_AUTOFREE(char *) alias = NULL;
+
+    /*
+     * save the alias to use when sending a DEVICE_REMOVED event after
+     * all other teardown is complete
+     */
+    if ((info = virDomainDeviceGetInfo(dev)) &&
+        VIR_STRDUP(alias, info->alias) < 0) {
+        return -1;
+    }
+    info = NULL;
+
     switch ((virDomainDeviceType)dev->type) {
+    case VIR_DOMAIN_DEVICE_CHR:
+        /* We must return directly after calling
+         * qemuDomainRemoveChrDevice because it is called directly
+         * from other places, so it must be completely self-contained
+         * and can't take advantage of any common code at the end of
+         * qemuDomainRemoveDevice().
+         */
+        return qemuDomainRemoveChrDevice(driver, vm, dev->data.chr, true);
+
+        /*
+         * all of the following qemuDomainRemove*Device() functions
+         * are (and must be) only called from this function, so any
+         * code that is common to them all can be pulled out and put
+         * into this function.
+         */
     case VIR_DOMAIN_DEVICE_DISK:
-        ret = qemuDomainRemoveDiskDevice(driver, vm, dev->data.disk);
+        if (qemuDomainRemoveDiskDevice(driver, vm, dev->data.disk) < 0)
+            return -1;
         break;
     case VIR_DOMAIN_DEVICE_CONTROLLER:
-        ret = qemuDomainRemoveControllerDevice(driver, vm, dev->data.controller);
+        if (qemuDomainRemoveControllerDevice(vm, dev->data.controller) < 0)
+            return -1;
         break;
     case VIR_DOMAIN_DEVICE_NET:
-        ret = qemuDomainRemoveNetDevice(driver, vm, dev->data.net);
+        if (qemuDomainRemoveNetDevice(driver, vm, dev->data.net) < 0)
+            return -1;
         break;
     case VIR_DOMAIN_DEVICE_HOSTDEV:
-        ret = qemuDomainRemoveHostDevice(driver, vm, dev->data.hostdev);
-        break;
-
-    case VIR_DOMAIN_DEVICE_CHR:
-        ret = qemuDomainRemoveChrDevice(driver, vm, dev->data.chr, true);
+        if (qemuDomainRemoveHostDevice(driver, vm, dev->data.hostdev) < 0)
+            return -1;
         break;
     case VIR_DOMAIN_DEVICE_RNG:
-        ret = qemuDomainRemoveRNGDevice(driver, vm, dev->data.rng);
+        if (qemuDomainRemoveRNGDevice(driver, vm, dev->data.rng) < 0)
+            return -1;
         break;
-
     case VIR_DOMAIN_DEVICE_MEMORY:
-        ret = qemuDomainRemoveMemoryDevice(driver, vm, dev->data.memory);
+        if (qemuDomainRemoveMemoryDevice(driver, vm, dev->data.memory) < 0)
+            return -1;
         break;
-
     case VIR_DOMAIN_DEVICE_SHMEM:
-        ret = qemuDomainRemoveShmemDevice(driver, vm, dev->data.shmem);
+        if (qemuDomainRemoveShmemDevice(driver, vm, dev->data.shmem) < 0)
+            return -1;
         break;
-
     case VIR_DOMAIN_DEVICE_INPUT:
-        ret = qemuDomainRemoveInputDevice(vm, dev->data.input);
+        if (qemuDomainRemoveInputDevice(vm, dev->data.input) < 0)
+            return -1;
         break;
-
     case VIR_DOMAIN_DEVICE_REDIRDEV:
-        ret = qemuDomainRemoveRedirdevDevice(driver, vm, dev->data.redirdev);
+        if (qemuDomainRemoveRedirdevDevice(driver, vm, dev->data.redirdev) < 0)
+            return -1;
         break;
-
     case VIR_DOMAIN_DEVICE_WATCHDOG:
-        ret = qemuDomainRemoveWatchdog(driver, vm, dev->data.watchdog);
+        if (qemuDomainRemoveWatchdog(vm, dev->data.watchdog) < 0)
+            return -1;
         break;
-
     case VIR_DOMAIN_DEVICE_VSOCK:
-        ret = qemuDomainRemoveVsockDevice(vm, dev->data.vsock);
+        if (qemuDomainRemoveVsockDevice(vm, dev->data.vsock) < 0)
+            return -1;
         break;
 
     case VIR_DOMAIN_DEVICE_NONE:
@@ -5322,7 +5307,11 @@ qemuDomainRemoveDevice(virQEMUDriverPtr driver,
                        virDomainDeviceTypeToString(dev->type));
         break;
     }
-    return ret;
+
+    event = virDomainEventDeviceRemovedNewFromObj(vm, alias);
+    virObjectEventStateQueue(driver->domainEventState, event);
+
+    return 0;
 }