Fix race in membership and ring consistency #112
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motiejus
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Without this change, membership and ring could be not in sync. Scenario: A - current node. B - alive (according to C). B - suspect (according to D). C - thinks B is faulty. D - thinks B is alive. At the same time: 1. C gossips A that B is faulty. A removes B to the membership list. 2. D gossips A that B is alive. A adds B from the membership list. Changes in the ring: 3. The lock on m.members is released, so updates on Ring due to (1) and (2) can execute in any order. In our example, the operations are reversed: 3.1. A adds B to the ring list due to (2). 3.2. A removes B to the ring list due to (1). Now B is in the membership list, but not in the ring. This is the second iteration of the change. First iteration did not introduce a new lock, but a new invariant: a goroutine needs to lock both memberlist and disseminator, lock memberlist first, then disseminator. However, the invariant caused requestAdminStats to fail on travis-ci, and I couldn't find out why.
motiejus
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lgtm |
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Oops, wrong button, sorry Motiejus. lgtm! |
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lgtm |
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lgtm |
motiejus
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Feb 23, 2016
Fix race in membership and ring consistency
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Without this change, membership and ring could be not in sync. Scenario:
A - current node.
B - alive (according to C).
B - suspect (according to D).
C - thinks B is faulty.
D - thinks B is alive.
At the same time:
Changes in the ring:
3. The lock on m.members is released, so updates on Ring due to (1) and
(2) can execute in any order. In our example, the operations are
reversed:
3.1. A adds B to the ring list due to (2).
3.2. A removes B to the ring list due to (1).
Now B is in the membership list, but not in the ring.
This is the second iteration of the change. First iteration did not
introduce a new lock, but a new invariant: a goroutine needs to lock
both memberlist and disseminator, lock memberlist first, then
disseminator. However, the invariant caused requestAdminStats to fail on
travis-ci, and I couldn't find out why.