vm: call after-shutdown cleanup also from vm.kill and vm.shutdown

Cleaning up after domain shutdown (domain-stopped and domain-shutdown
events) relies on libvirt events which may be unreliable in some cases
(events may be processed with some delay, of if libvirt was restarted in
the meantime, may not happen at all). So, instead of ensuring only
proper ordering between shutdown cleanup and next startup, also trigger
the cleanup when we know for sure domain isn't running:
 - at vm.kill() - after libvirt confirms domain was destroyed
 - at vm.shutdown(wait=True) - after successful shutdown
 - at vm.remove_from_disk() - after ensuring it isn't running but just
 before actually removing it

This fixes various race conditions:
 - qvm-kill && qvm-remove: remove could happen before shutdown cleanup
 was done and storage driver would be confused about that
 - qvm-shutdown --wait && qvm-clone: clone could happen before new content was
 commited to the original volume, making the copy of previous VM state
(and probably more)

Previously it wasn't such a big issue on default configuration, because
LVM driver was fully synchronous, effectively blocking the whole qubesd
for the time the cleanup happened.

To avoid code duplication, factor out _ensure_shutdown_handled function
calling actual cleanup (and possibly canceling one called with libvirt
event). Note that now, "Duplicated stopped event from libvirt received!"
warning may happen in normal circumstances, not only because of some
bug.

It is very important that post-shutdown cleanup happen when domain is
not running. To ensure that, take startup_lock and under it 1) ensure
its halted and only then 2) execute the cleanup. This isn't necessary
when removing it from disk, because its already removed from the
collection at that time, which also avoids other calls to it (see also
"vm/dispvm: fix DispVM cleanup" commit).
Actually, taking the startup_lock in remove_from_disk function would
cause a deadlock in DispVM auto cleanup code:
 - vm.kill (or other trigger for the cleanup)
   - vm.startup_lock acquire   <====
     - vm._ensure_shutdown_handled
       - domain-shutdown event
         - vm._auto_cleanup (in DispVM class)
           - vm.remove_from_disk
             - cannot take vm.startup_lock again

qubes/vm/qubesvm.py

@@ -878,6 +878,36 @@ def on_property_pre_del_autostart(self, event, name, oldvalue=None):
     # methods for changing domain state
     #
 
+    @asyncio.coroutine
+    def _ensure_shutdown_handled(self):
+        '''Make sure previous shutdown is fully handled.
+        MUST NOT be called when domain is running.
+        '''
+        with (yield from self._domain_stopped_lock):
+            # Don't accept any new stopped event's till a new VM has been
+            # created. If we didn't received any stopped event or it wasn't
+            # handled yet we will handle this in the next lines.
+            self._domain_stopped_event_received = True
+
+            if self._domain_stopped_future is not None:
+                # Libvirt stopped event was already received, so cancel the
+                # future. If it didn't generate the Qubes events yet we
+                # will do it below.
+                self._domain_stopped_future.cancel()
+                self._domain_stopped_future = None
+
+            if not self._domain_stopped_event_handled:
+                # No Qubes domain-stopped events have been generated yet.
+                # So do this now.
+
+                # Set this immediately such that we don't generate events
+                # twice if an exception gets thrown.
+                self._domain_stopped_event_handled = True
+
+                yield from self.fire_event_async('domain-stopped')
+                yield from self.fire_event_async('domain-shutdown')
+
+
     @asyncio.coroutine
     def start(self, start_guid=True, notify_function=None,
             mem_required=None):
@@ -894,29 +924,7 @@ def start(self, start_guid=True, notify_function=None,
             if self.get_power_state() != 'Halted':
                 return self
 
-            with (yield from self._domain_stopped_lock):
-                # Don't accept any new stopped event's till a new VM has been
-                # created. If we didn't received any stopped event or it wasn't
-                # handled yet we will handle this in the next lines.
-                self._domain_stopped_event_received = True
-
-                if self._domain_stopped_future is not None:
-                    # Libvirt stopped event was already received, so cancel the
-                    # future. If it didn't generate the Qubes events yet we
-                    # will do it below.
-                    self._domain_stopped_future.cancel()
-                    self._domain_stopped_future = None
-
-                if not self._domain_stopped_event_handled:
-                    # No Qubes domain-stopped events have been generated yet.
-                    # So do this now.
-
-                    # Set this immediately such that we don't generate events
-                    # twice if an exception gets thrown.
-                    self._domain_stopped_event_handled = True
-
-                    yield from self.fire_event_async('domain-stopped')
-                    yield from self.fire_event_async('domain-shutdown')
+            yield from self._ensure_shutdown_handled()
 
             self.log.info('Starting {}'.format(self.name))
 
@@ -1030,8 +1038,8 @@ def on_libvirt_domain_stopped(self):
             return
 
         if self._domain_stopped_event_received:
-            self.log.warning('Duplicated stopped event from libvirt received!')
-            # ignore this unexpected event
+            # ignore this event - already triggered by shutdown(), kill(),
+            # or subsequent start()
             return
 
         self._domain_stopped_event_received = True
@@ -1088,8 +1096,12 @@ def shutdown(self, force=False, wait=False, timeout=None):
             while timeout > 0 and not self.is_halted():
                 yield from asyncio.sleep(0.25)
                 timeout -= 0.25
-            if not self.is_halted():
-                raise qubes.exc.QubesVMShutdownTimeoutError(self)
+            with (yield from self.startup_lock):
+                if self.is_halted():
+                    # make sure all shutdown tasks are completed
+                    yield from self._ensure_shutdown_handled()
+                else:
+                    raise qubes.exc.QubesVMShutdownTimeoutError(self)
 
         return self
 
@@ -1104,13 +1116,17 @@ def kill(self):
         if not self.is_running() and not self.is_paused():
             raise qubes.exc.QubesVMNotStartedError(self)
 
-        try:
-            self.libvirt_domain.destroy()
-        except libvirt.libvirtError as e:
-            if e.get_error_code() == libvirt.VIR_ERR_OPERATION_INVALID:
-                raise qubes.exc.QubesVMNotStartedError(self)
-            else:
-                raise
+        with (yield from self.startup_lock):
+            try:
+                self.libvirt_domain.destroy()
+            except libvirt.libvirtError as e:
+                if e.get_error_code() == libvirt.VIR_ERR_OPERATION_INVALID:
+                    raise qubes.exc.QubesVMNotStartedError(self)
+                else:
+                    raise
+
+            # make sure all shutdown tasks are completed
+            yield from self._ensure_shutdown_handled()
 
         return self
 
@@ -1477,6 +1493,12 @@ def remove_from_disk(self):
                 "Can't remove VM {!s}, beacuse it's in state {!r}.".format(
                     self, self.get_power_state()))
 
+        # make sure shutdown is handled before removing anything, but only if
+        # handling is pending; if not, we may be called from within
+        # domain-shutdown event (DispVM._auto_cleanup), which would deadlock
+        if not self._domain_stopped_event_handled:
+            yield from self._ensure_shutdown_handled()
+
         yield from self.fire_event_async('domain-remove-from-disk')
         try:
             # TODO: make it async?