Sergey Zolotukhin 612a141660 raft: Fix race condition on override_snapshot_thresholds. ...

When the server_impl::applier_fiber is paused by a co_await at line raft/server.cc:1375:
```
co_await override_snapshot_thresholds();
```
a new snapshot may be applied, which updates the actual values of the log's last applied
and snapshot indexes. As a result, the new snapshot index could become higher than the
old value stored in _applied_idx at line raft/server.cc:1365, leading to an assertion
failure in log::last_conf_for().
Since error injection is disabled in release builds, this issue does not affect production releases.

This issue was introduced in the following commit
9dfa041fe1,
when error injection was added to override the log snapshot configuration parameters.

How to reproduce:

1. Build debug version of randomized_nemesis_test
```
ninja-build build/debug/test/raft/randomized_nemesis_test
```
2. Run
```
parallel --halt now,fail=1 -j20 'build/debug/test/raft/randomized_nemesis_test \
--run_test=test_frequent_snapshotting  -- -c2 -m2G --overprovisioned --unsafe-bypass-fsync 1 \
--kernel-page-cache 1 --blocked-reactor-notify-ms 2000000  --default-log-level \
trace > tmp/logs/eraseme_{}.log  2>&1 && rm tmp/logs/eraseme_{}.log' ::: {1..1000}
```

Fixes scylladb/scylladb#20363

Closes scylladb/scylladb#20555

2024-09-12 16:19:27 +02:00

84 KiB

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