[KUDU-3010] unsafe_change_config can lead to a crash

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: consensus, ops-tooling
• Assignee: Unassigned
• Reporter: Andrew Wong
• Created: 26/Nov/19 20:53
• Updated: 28/Nov/19 03:14

Description

I've seen a case of running the unsafe_change_config tool, per the steps laid out in the "Bringing a tablet that has lost a majority of replicas" steps, crashing a tserver with the following error:

I1028 08:24:31.241361 38436 raft_consensus.cc:684] T b90b0429806747a6b993d8543ab5fd50 P f344ade17ed94072b8839007ccc7570a [term 40 FOLLOWER]: Illegal state: RaftConfig change currently pending. Only one is allowed at a time.
W1028 08:24:31.241379 38436 raft_consensus.cc:1373] T b90b0429806747a6b993d8543ab5fd50 P f344ade17ed94072b8839007ccc7570a [term 40 FOLLOWER]: Could not prepare transaction for op 34.48 and following 69 ops. Status for this op: Illegal state: RaftConfig change currently pending. Only one is allowed at a time.
I1028 08:26:07.300520 38436 raft_consensus.cc:1058] T a6bfa86e43b74cfaa6feba4631879251 P f344ade17ed94072b8839007ccc7570a [term 17 FOLLOWER]: Refusing update from remote peer f1a7fb14b7b44a5c8b31e93114d79a8d: Log matching property violated. Preceding OpId in replica: term: 15 index: 93. Preceding OpId from leader: term: 17 index: 112. (index mismatch)
I1028 08:26:07.301476 38436 raft_consensus.cc:2819] T a6bfa86e43b74cfaa6feba4631879251 P f344ade17ed94072b8839007ccc7570a [term 17 NON_PARTICIPANT]: Allowing unsafe config change even though there is a pending config! Existing pending config: opid_index: 95 OBSOLETE_local: false peers { permanent_uuid: "7875cc5598a44bd893998cba7bd2cc47" member_type: VOTER last_known_addr{ host: "foo01.server.net" port: 7050 }
attrs{ promote: false }
} peers { permanent_uuid: "f1a7fb14b7b44a5c8b31e93114d79a8d" member_type: NON_VOTER last_known_addr{ host: "foo04.server.net" port: 7050 }
attrs{ promote: true }
} unsafe_config_change: true; New pending config: opid_index: 96 OBSOLETE_local: false peers { permanent_uuid: "7875cc5598a44bd893998cba7bd2cc47" member_type: VOTER last_known_addr{ host: "foo01.server.net" port: 7050 }
attrs{ promote: false }
} peers { permanent_uuid: "f1a7fb14b7b44a5c8b31e93114d79a8d" member_type: NON_VOTER last_known_addr{ host: "foo04.server.net" port: 7050 }
attrs{ promote: true }
} peers { permanent_uuid: "231e6fdad22647978c9a76c07407da4c" member_type: NON_VOTER last_known_addr{ host: "foo02.server.net" port: 7050 }
attrs{ promote: true }
} unsafe_config_change: true
F1028 08:26:07.302338 38436 pending_rounds.cc:179] Check failed: _s.ok() Bad status: Corruption: New operation's term is not >= than the previous op's term. Current: 14.94. Previous: 15.93

It seems like the tool is permitting the persistence of a bad op, considering there's already a config change in flight.