Add lock per share for cinder nfs mount/umount

With cinder configured as glance store and nfs as cinder backend,
if we create multiple images concurrently into the same share,
there might be race conditions.
This patch ensures a lock per export to avoid the race conditions.

This patch also introduces a reference counting mechamism for unmounting
which will unmount the share if no active thread/process is using it.

Closes-Bug: #1870289

Change-Id: I9197f64e29a0ae2e0a58186f1a70aa134f7f1db6

2 files changed, 370 insertions, 0 deletions

diff --git a/glance_store/common/fs_mount.py b/glance_store/common/fs_mount.py
new file mode 100644
index 0000000..3983f8b
--- /dev/null
+++ b/glance_store/common/fs_mount.py
@@ -0,0 +1,366 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import collections
+import contextlib
+import logging
+import os
+import socket
+import threading
+
+from oslo_concurrency import processutils
+from oslo_config import cfg
+
+from glance_store import exceptions
+from glance_store.i18n import _LE, _LW
+
+
+LOG = logging.getLogger(__name__)
+
+HOST = socket.gethostname()
+CONF = cfg.CONF
+
+
+class HostMountStateManagerMeta(type):
+    _instance = {}
+
+    def __call__(cls, *args, **kwargs):
+        if cls not in cls._instance:
+            cls._instance[cls] = super(
+                HostMountStateManagerMeta, cls).__call__(*args, **kwargs)
+        return cls._instance[cls]
+
+
+class _HostMountStateManager(metaclass=HostMountStateManagerMeta):
+    """A global manager of filesystem mounts.
+
+    _HostMountStateManager manages a _HostMountState object for the current
+    glance node. Primarily it creates one on object initialization and returns
+    it via get_state().
+
+    _HostMountStateManager manages concurrency itself. Independent callers do
+    not need to consider interactions between multiple _HostMountStateManager
+    calls when designing their own locking.
+
+    """
+    # Reset state of global _HostMountStateManager
+    state = None
+    use_count = 0
+
+    # Guards both state and use_count
+    cond = threading.Condition()
+
+    def __init__(self, host):
+        """Initialise a new _HostMountState
+
+        We will block before creating a new state until all operations
+        using a previous state have completed.
+
+        :param host: host
+        """
+        # Wait until all operations using a previous state are
+        # complete before initialising a new one. Note that self.state is
+        # already None, set either by initialisation or by host_down. This
+        # means the current state will not be returned to any new callers,
+        # and use_count will eventually reach zero.
+        # We do this to avoid a race between _HostMountState initialisation
+        # and an on-going mount/unmount operation
+        self.host = host
+        while self.use_count != 0:
+            self.cond.wait()
+
+        # Another thread might have initialised state while we were
+        # waiting
+        if self.state is None:
+            LOG.debug('Initialising _HostMountState')
+            self.state = _HostMountState()
+            backends = []
+            enabled_backends = CONF.enabled_backends
+            if enabled_backends:
+                for backend in enabled_backends:
+                    if enabled_backends[backend] == 'cinder':
+                        backends.append(backend)
+            else:
+                backends.append('glance_store')
+
+            for backend in backends:
+                mountpoint = getattr(CONF, backend).cinder_mount_point_base
+                # This is currently designed for cinder nfs backend only.
+                # Later can be modified to work with other *fs backends.
+                mountpoint = os.path.join(mountpoint, 'nfs')
+                # There will probably be the same rootwrap file for all stores,
+                # generalizing this will be done in a later refactoring
+                rootwrap = getattr(CONF, backend).rootwrap_config
+                rootwrap = ('sudo glance-rootwrap %s' % rootwrap)
+                dirs = []
+                # fetch the directories in the mountpoint path
+                if os.path.isdir(mountpoint):
+                    dirs = os.listdir(mountpoint)
+                else:
+                    continue
+                if not dirs:
+                    return
+                for dir in dirs:
+                    # for every directory in the mountpath, we
+                    # unmount it (if mounted) and remove it
+                    dir = os.path.join(mountpoint, dir)
+                    with self.get_state() as mount_state:
+                        if os.path.exists(dir) and not os.path.ismount(dir):
+                            try:
+                                os.rmdir(dir)
+                            except Exception as ex:
+                                LOG.debug(
+                                    "Couldn't remove directory"
+                                    "%(mountpoint)s: %(reason)s",
+                                    {'mountpoint': mountpoint,
+                                     'reason': ex})
+                        else:
+                            mount_state.umount(None, dir, HOST, rootwrap)
+
+    @contextlib.contextmanager
+    def get_state(self):
+        """Return the current mount state.
+
+        _HostMountStateManager will not permit a new state object to be
+        created while any previous state object is still in use.
+
+        :rtype: _HostMountState
+        """
+
+        # We hold the instance lock here so that if a _HostMountState is
+        # currently initialising we'll wait for it to complete rather than
+        # fail.
+        with self.cond:
+            state = self.state
+            if state is None:
+                LOG.error('Host not initialized')
+                raise exceptions.HostNotInitialized(host=self.host)
+            self.use_count += 1
+        try:
+            LOG.debug('Got _HostMountState')
+            yield state
+        finally:
+            with self.cond:
+                self.use_count -= 1
+                self.cond.notify_all()
+
+
+class _HostMountState(object):
+    """A data structure recording all managed mountpoints and the
+    attachments in use for each one. _HostMountState ensures that the glance
+    node only attempts to mount a single mountpoint in use by multiple
+    attachments once, and that it is not unmounted until it is no longer in use
+    by any attachments.
+
+    Callers should not create a _HostMountState directly, but should obtain
+    it via:
+
+      with mount.get_manager().get_state() as state:
+        state.mount(...)
+
+    _HostMountState manages concurrency itself. Independent callers do not need
+    to consider interactions between multiple _HostMountState calls when
+    designing their own locking.
+    """
+
+    class _MountPoint(object):
+        """A single mountpoint, and the set of attachments in use on it."""
+        def __init__(self):
+            # A guard for operations on this mountpoint
+            # N.B. Care is required using this lock, as it will be deleted
+            # if the containing _MountPoint is deleted.
+            self.lock = threading.Lock()
+
+            # The set of attachments on this mountpoint.
+            self.attachments = set()
+
+        def add_attachment(self, vol_name, host):
+            self.attachments.add((vol_name, host))
+
+        def remove_attachment(self, vol_name, host):
+            self.attachments.remove((vol_name, host))
+
+        def in_use(self):
+            return len(self.attachments) > 0
+
+    def __init__(self):
+        """Initialise _HostMountState"""
+
+        self.mountpoints = collections.defaultdict(self._MountPoint)
+
+    @contextlib.contextmanager
+    def _get_locked(self, mountpoint):
+        """Get a locked mountpoint object
+
+        :param mountpoint: The path of the mountpoint whose object we should
+                           return.
+        :rtype: _HostMountState._MountPoint
+        """
+        while True:
+            mount = self.mountpoints[mountpoint]
+            with mount.lock:
+                if self.mountpoints[mountpoint] is mount:
+                    yield mount
+                    break
+
+    def mount(self, fstype, export, vol_name, mountpoint, host,
+              rootwrap_helper, options):
+        """Ensure a mountpoint is available for an attachment, mounting it
+        if necessary.
+
+        If this is the first attachment on this mountpoint, we will mount it
+        with:
+
+          mount -t <fstype> <options> <export> <mountpoint>
+
+        :param fstype: The filesystem type to be passed to mount command.
+        :param export: The type-specific identifier of the filesystem to be
+                       mounted. e.g. for nfs 'host.example.com:/mountpoint'.
+        :param vol_name: The name of the volume on the remote filesystem.
+        :param mountpoint: The directory where the filesystem will be
+                           mounted on the local compute host.
+        :param host: The host the volume will be attached to.
+        :param options: An arbitrary list of additional arguments to be
+                        passed to the mount command immediate before export
+                        and mountpoint.
+        """
+
+        LOG.debug('_HostMountState.mount(fstype=%(fstype)s, '
+                  'export=%(export)s, vol_name=%(vol_name)s, %(mountpoint)s, '
+                  'options=%(options)s)',
+                  {'fstype': fstype, 'export': export, 'vol_name': vol_name,
+                   'mountpoint': mountpoint, 'options': options})
+        with self._get_locked(mountpoint) as mount:
+            if not os.path.ismount(mountpoint):
+                LOG.debug('Mounting %(mountpoint)s',
+                          {'mountpoint': mountpoint})
+
+                os.makedirs(mountpoint)
+
+                mount_cmd = ['mount', '-t', fstype]
+                if options is not None:
+                    mount_cmd.extend(options)
+                mount_cmd.extend([export, mountpoint])
+
+                try:
+                    processutils.execute(*mount_cmd, run_as_root=True,
+                                         root_helper=rootwrap_helper)
+                except Exception:
+                    # Check to see if mountpoint is mounted despite the error
+                    # eg it was already mounted
+                    if os.path.ismount(mountpoint):
+                        # We're not going to raise the exception because we're
+                        # in the desired state anyway. However, this is still
+                        # unusual so we'll log it.
+                        LOG.exception(_LE('Error mounting %(fstype)s export '
+                                          '%(export)s on %(mountpoint)s. '
+                                          'Continuing because mountpount is '
+                                          'mounted despite this.'),
+                                      {'fstype': fstype, 'export': export,
+                                       'mountpoint': mountpoint})
+
+                    else:
+                        # If the mount failed there's no reason for us to keep
+                        # a record of it. It will be created again if the
+                        # caller retries.
+
+                        # Delete while holding lock
+                        del self.mountpoints[mountpoint]
+
+                        raise
+
+            mount.add_attachment(vol_name, host)
+
+        LOG.debug('_HostMountState.mount() for %(mountpoint)s '
+                  'completed successfully',
+                  {'mountpoint': mountpoint})
+
+    def umount(self, vol_name, mountpoint, host, rootwrap_helper):
+        """Mark an attachment as no longer in use, and unmount its mountpoint
+        if necessary.
+
+        :param vol_name: The name of the volume on the remote filesystem.
+        :param mountpoint: The directory where the filesystem is be
+                           mounted on the local compute host.
+        :param host: The host the volume was attached to.
+        """
+        LOG.debug('_HostMountState.umount(vol_name=%(vol_name)s, '
+                  'mountpoint=%(mountpoint)s)',
+                  {'vol_name': vol_name, 'mountpoint': mountpoint})
+        with self._get_locked(mountpoint) as mount:
+            try:
+                mount.remove_attachment(vol_name, host)
+            except KeyError:
+                LOG.warning(_LW("Request to remove attachment "
+                                "(%(vol_name)s, %(host)s) from "
+                                "%(mountpoint)s, but we don't think it's in "
+                                "use."),
+                            {'vol_name': vol_name, 'host': host,
+                             'mountpoint': mountpoint})
+
+            if not mount.in_use():
+                mounted = os.path.ismount(mountpoint)
+
+                if mounted:
+                    mounted = self._real_umount(mountpoint, rootwrap_helper)
+
+                # Delete our record entirely if it's unmounted
+                if not mounted:
+                    del self.mountpoints[mountpoint]
+
+            LOG.debug('_HostMountState.umount() for %(mountpoint)s '
+                      'completed successfully',
+                      {'mountpoint': mountpoint})
+
+    def _real_umount(self, mountpoint, rootwrap_helper):
+        # Unmount and delete a mountpoint.
+        # Return mount state after umount (i.e. True means still mounted)
+        LOG.debug('Unmounting %(mountpoint)s', {'mountpoint': mountpoint})
+
+        try:
+            processutils.execute('umount', mountpoint, run_as_root=True,
+                                 attempts=3, delay_on_retry=True,
+                                 root_helper=rootwrap_helper)
+        except processutils.ProcessExecutionError as ex:
+            LOG.error(_LE("Couldn't unmount %(mountpoint)s: %(reason)s"),
+                      {'mountpoint': mountpoint, 'reason': ex})
+
+        if not os.path.ismount(mountpoint):
+            try:
+                os.rmdir(mountpoint)
+            except Exception as ex:
+                LOG.error(_LE("Couldn't remove directory %(mountpoint)s: "
+                              "%(reason)s"),
+                          {'mountpoint': mountpoint,
+                           'reason': ex})
+            return False
+
+        return True
+
+
+__manager__ = _HostMountStateManager(HOST)
+
+
+def mount(fstype, export, vol_name, mountpoint, host, rootwrap_helper,
+          options=None):
+    """A convenience wrapper around _HostMountState.mount()"""
+
+    with __manager__.get_state() as mount_state:
+        mount_state.mount(fstype, export, vol_name, mountpoint, host,
+                          rootwrap_helper, options)
+
+
+def umount(vol_name, mountpoint, host, rootwrap_helper):
+    """A convenience wrapper around _HostMountState.umount()"""
+
+    with __manager__.get_state() as mount_state:
+        mount_state.umount(vol_name, mountpoint, host, rootwrap_helper)
diff --git a/glance_store/common/utils.py b/glance_store/common/utils.py
index 49acccb..0ee40f7 100644
--- a/glance_store/common/utils.py
+++ b/glance_store/common/utils.py
@@ -21,6 +21,8 @@ System-level utilities and helper functions.
 import logging
 import uuid
 
+from oslo_concurrency import lockutils
+
 try:
     from eventlet import sleep
 except ImportError:
@@ -31,6 +33,8 @@ from glance_store.i18n import _
 
 LOG = logging.getLogger(__name__)
 
+synchronized = lockutils.synchronized_with_prefix('glance_store-')
+
 
 def is_uuid_like(val):
     """Returns validation of a value as a UUID.