|
1 |
Introduction:
|
|
2 |
|
|
3 |
This document describes lock order dependencies in Ganeti.
|
|
4 |
It is divided by functional sections
|
|
5 |
|
|
6 |
|
|
7 |
Opcode Execution Locking:
|
|
8 |
|
|
9 |
These locks are declared by Logical Units (LUs) (in cmdlib.py) and acquired by
|
|
10 |
the Processor (in mcpu.py) with the aid of the Ganeti Locking Library
|
|
11 |
(locking.py). They are acquired in the following order:
|
|
12 |
|
|
13 |
* BGL: this is the Big Ganeti Lock, it exists for retrocompatibility. New LUs
|
|
14 |
acquire it in a shared fashion, and are able to execute all toghether
|
|
15 |
(baring other lock waits) while old LUs acquire it exclusively and can only
|
|
16 |
execute one at a time, and not at the same time with new LUs.
|
|
17 |
* Instance locks: can be declared in ExpandNames() o DeclareLocks() by an LU,
|
|
18 |
and have the same name as the instance itself. They are acquired as a set.
|
|
19 |
Internally the locking library acquired them in alphabetical order.
|
|
20 |
* Node locks: can be declared in ExpandNames() o DeclareLocks() by an LU, and
|
|
21 |
have the same name as the node itself. They are acquired as a set.
|
|
22 |
Internally the locking library acquired them in alphabetical order. Given
|
|
23 |
this order it's possible to safely acquire a set of instances, and then the
|
|
24 |
nodes they reside on.
|
|
25 |
|
|
26 |
The ConfigWriter (in config.py) is also protected by a SharedLock, which is
|
|
27 |
shared by functions that read the config and acquired exclusively by functions
|
|
28 |
that modify it. Since the ConfigWriter calls rpc.call_upload_file to all nodes
|
|
29 |
to distribute the config without holding the node locks, this call must be able
|
|
30 |
to execute on the nodes in parallel with other operations (but not necessarily
|
|
31 |
concurrently with itself on the same file, as inside the ConfigWriter this is
|
|
32 |
called with the internal config lock held.
|
|
33 |
|