lock fstab with ansible's FileLock to avoid race condition

changelogs/fragments/161-fix-115_race_condition_in_mount_module.yml

@@ -0,0 +1,6 @@
+---
+bugfixes:
+  - mount - fix a race condition that might result in unknown/unexpected fstab
+    state when running the module on several inventory hostnames adressing the
+    same host. Lock it with ansible.module_utils.common.file.FileLock.lock_file()
+    (https://github.com/ansible-collections/ansible.posix/issues/115).

plugins/modules/mount.py

@@ -193,6 +193,7 @@ from ansible_collections.ansible.posix.plugins.module_utils.mount import ismount
 from ansible.module_utils.six import iteritems
 from ansible.module_utils._text import to_bytes, to_native
 from ansible.module_utils.parsing.convert_bool import boolean
+from ansible.module_utils.common.file import FileLock, LockTimeout
 
 
 def write_fstab(module, lines, path):
@@ -763,6 +764,14 @@ def main():
     name = module.params['path']
     changed = False
 
+    lock_timeout = 2
+    lock_tempdir = '/tmp'
+    lock_message = 'another instance of the module holds the %s lock' % os.path.basename(args['fstab'])
+
+    _fstab = FileLock()
+    try:
+        with _fstab.lock_file(args['fstab'], lock_tempdir, lock_timeout):
+
             if state == 'absent':
                 name, changed = unset_mount(module, args)
 
@@ -863,6 +872,9 @@ def main():
             else:
                 module.fail_json(msg='Unexpected position reached')
 
+    except LockTimeout:
+        module.fail_json(msg=lock_message)
+
     # If the managed node is Solaris, convert the boot value type to Boolean
     #  to match the type of return value with the module argument.
     if platform.system().lower() == 'sunos':