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raft: server: fix bad_variant_access in modify_config

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`modify_config` would call `execute_modify_config` or
`_rpc->send_modify_config`, which returned a reply of type
`add_entry_reply`. This is a variant of 3 options: `entry_id`,
`not_a_leader`, or `commit_status_unknown`. The code would check
for the `entry_id` option and otherwise assume that it was `not_a_leader`.
During nemesis testing however, the reply was sometimes
`commit_status_unknown`, which caused a `bad_variant_access` exception
during `std::get` call. Fix this.

There is a similar piece of code in `add_entry`, but there it should be
impossible to obtain `commit_status_unknown` even though the types don't
enforce it. Make it more explicit with a comment and an assertion.
This commit is contained in:
Kamil Braun
2022-05-10 18:52:44 +02:00
parent 6a3494442e
commit 5e06d0ad6f
1 changed files with 13 additions and 2 deletions
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15
raft/server.cc
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@@ -502,8 +502,15 @@ future<> server_impl::add_entry(command command, wait_type type, seastar::abort_
}();
if (std::holds_alternative<raft::entry_id>(reply)) {
co_return co_await wait_for_entry(std::get<raft::entry_id>(reply), type, as);
} else if (std::holds_alternative<raft::commit_status_unknown>(reply)) {
// It should be impossible to obtain `commit_status_unknown` here
// because neither `execute_add_entry` nor `send_add_entry` wait for the entry
// to be committed/applied.
on_internal_error(logger, "add_entry: `execute_add_entry` or `send_add_entry`"
" returned `commit_status_unknown`");
} else {
leader = std::get<raft::not_a_leader>(reply).leader;
}
leader = std::get<raft::not_a_leader>(reply).leader;
}
}
}
@@ -596,7 +603,11 @@ future<> server_impl::modify_config(std::vector<server_address> add, std::vector
// See also #9981.
co_return;
}
leader = std::get<raft::not_a_leader>(reply).leader;
if (auto nal = std::get_if<raft::not_a_leader>(&reply)) {
leader = nal->leader;
} else {
throw std::get<raft::commit_status_unknown>(reply);
}
}
}
}