Fix locking in store rollback#2103
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fix_store_rollback@17866 aka 20210122.15 vs master ewma over 50 builds from 17216 to 17861 |
eddyashton
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Jan 22, 2021
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Store::rollback() acquires and holds the maps lock for its entire execution, and the version lock several times (twice explicitly, one or two more times indirectly via current_version()). The term is updated under the first acquisition, but the version (and other elements of state) are only updated in the final acquisition.
As a result, a transaction starting in the middle of a rollback() could when it captures current_txid() grab an incorrect (term, version) pair. Making all store state changes atomically under a single acquisition of the version lock fixes that.