[Tarantool-patches] [PATCH v19 2/3] qsync: order access to the limbo terms

[Cyrill Gorcunov]

On Fri, Oct 01, 2021 at 03:37:18PM +0300, Serge Petrenko wrote:
> Shouldn't we guard limbo->owner as well?
> Otherwise you may start writing confirm for an old leader once promote for a
> new one is already in progress.
> 
> I don't remember us discussing this before, so, maybe I'm just confused.

Seems I still don't follow. Look, currently limbo::owner_id is assigned
from the one place:

txn_limbo_process_core
  txn_limbo_process_begin(limbo)
    txn_limbo_read_demote | txn_limbo_read_promote
      ...
      limbo->owner_id = replica_id;

The txn_limbo_process_core is called from console (via box.ctl.promote|demote
commands) or via applier. When it comes from console then we still take the
lock before write into the journal

static void
box_issue_promote(uint32_t prev_leader_id, int64_t promote_lsn)
{
	struct raft *raft = box_raft();
	assert(raft->volatile_term == raft->term);
	assert(promote_lsn >= 0);
	struct synchro_request req = {
		.type = IPROTO_RAFT_PROMOTE,
		.replica_id = prev_leader_id,
		.origin_id = instance_id,
		.lsn = promote_lsn,
		.term = raft->term,
	};
-->	txn_limbo_process_begin(&txn_limbo);
-->	txn_limbo_write_promote(&txn_limbo, req.lsn, req.term);
	txn_limbo_process_core(&txn_limbo, &req);
	assert(txn_limbo_is_empty(&txn_limbo));
	txn_limbo_process_commit(&txn_limbo);
}

thus console commands and applier are serialized. Or I miss something
obvious?