KVM: Check instances for actual liveness

Currently if we find a live process with the pid we saved we assume kvm
is alive. What could happen, though, is that the pidfile has been
reused.

In order to avoid that we change the check to make sure, everywhere,
that the process we see is our actual kvm process. In order to do so we
open its cmdline, and check that it contains the correct instance name
in the -name argument passed to kvm.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

lib/hypervisor/hv_kvm.py

@@ -107,13 +107,69 @@ class KVMHypervisor(hv_base.BaseHypervisor):
     """
     return utils.PathJoin(cls._PIDS_DIR, instance_name)
 
+  @classmethod
+  def _InstancePidInfo(cls, pid):
+    """Check pid file for instance information.
+
+    Check that a pid file is associated with an instance, and retrieve
+    information from its command line.
+
+    @type pid: string or int
+    @param pid: process id of the instance to check
+    @rtype: tuple
+    @return: (instance_name, memory, vcpus)
+    @raise errors.HypervisorError: when an instance cannot be found
+
+    """
+    alive = utils.IsProcessAlive(pid)
+    if not alive:
+      raise errors.HypervisorError("Cannot get info for pid %s" % pid)
+
+    cmdline_file = utils.PathJoin("/proc", str(pid), "cmdline")
+    try:
+      cmdline = utils.ReadFile(cmdline_file)
+    except EnvironmentError, err:
+      raise errors.HypervisorError("Can't open cmdline file for pid %s: %s" %
+                                   (pid, err))
+
+    instance = None
+    memory = 0
+    vcpus = 0
+
+    arg_list = cmdline.split('\x00')
+    while arg_list:
+      arg =  arg_list.pop(0)
+      if arg == "-name":
+        instance = arg_list.pop(0)
+      elif arg == "-m":
+        memory = int(arg_list.pop(0))
+      elif arg == "-smp":
+        vcpus = int(arg_list.pop(0))
+
+    if instance is None:
+      raise errors.HypervisorError("Pid %s doesn't contain a ganeti kvm"
+                                   " instance" % pid)
+
+    return (instance, memory, vcpus)
+
   def _InstancePidAlive(self, instance_name):
-    """Returns the instance pid and pidfile
+    """Returns the instance pidfile, pid, and liveness.
+
+    @type instance_name: string
+    @param instance_name: instance name
+    @rtype: tuple
+    @return: (pid file name, pid, liveness)
 
     """
     pidfile = self._InstancePidFile(instance_name)
     pid = utils.ReadPidFile(pidfile)
-    alive = utils.IsProcessAlive(pid)
+
+    alive = False
+    try:
+      cmd_instance = self._InstancePidInfo(pid)[0]
+      alive = (cmd_instance == instance_name)
+    except errors.HypervisorError:
+      pass
 
     return (pidfile, pid, alive)
 
@@ -250,8 +306,7 @@ class KVMHypervisor(hv_base.BaseHypervisor):
     """
     result = []
     for name in os.listdir(self._PIDS_DIR):
-      filename = utils.PathJoin(self._PIDS_DIR, name)
-      if utils.IsProcessAlive(utils.ReadPidFile(filename)):
+      if self._InstancePidAlive(name)[2]:
         result.append(name)
     return result
 
@@ -268,26 +323,10 @@ class KVMHypervisor(hv_base.BaseHypervisor):
     if not alive:
       return None
 
-    cmdline_file = utils.PathJoin("/proc", str(pid), "cmdline")
-    try:
-      cmdline = utils.ReadFile(cmdline_file)
-    except EnvironmentError, err:
-      raise errors.HypervisorError("Failed to list instance %s: %s" %
-                                   (instance_name, err))
-
-    memory = 0
-    vcpus = 0
+    _, memory, vcpus = self._InstancePidInfo(pid)
     stat = "---b-"
     times = "0"
 
-    arg_list = cmdline.split('\x00')
-    while arg_list:
-      arg =  arg_list.pop(0)
-      if arg == '-m':
-        memory = int(arg_list.pop(0))
-      elif arg == '-smp':
-        vcpus = int(arg_list.pop(0))
-
     return (instance_name, pid, memory, vcpus, stat, times)
 
   def GetAllInstancesInfo(self):
@@ -298,15 +337,12 @@ class KVMHypervisor(hv_base.BaseHypervisor):
     """
     data = []
     for name in os.listdir(self._PIDS_DIR):
-      filename = utils.PathJoin(self._PIDS_DIR, name)
-      if utils.IsProcessAlive(utils.ReadPidFile(filename)):
-        try:
-          info = self.GetInstanceInfo(name)
-        except errors.HypervisorError:
-          continue
-        if info:
-          data.append(info)
-
+      try:
+        info = self.GetInstanceInfo(name)
+      except errors.HypervisorError:
+        continue
+      if info:
+        data.append(info)
     return data
 
   def _GenerateKVMRuntime(self, instance, block_devices):
@@ -588,7 +624,7 @@ class KVMHypervisor(hv_base.BaseHypervisor):
       else:
         self._CallMonitorCommand(instance.name, 'system_powerdown')
 
-    if not utils.IsProcessAlive(pid):
+    if not self._InstancePidAlive(instance.name)[2]:
       self._RemoveInstanceRuntimeFiles(pidfile, instance.name)
       return True
     else: