resolve: exit from loop for transactions when transactions has been regenerated

Fixes #37458.

(cherry picked from commit 5814acca9aa4354d121de4bf174851f092a6b643)

Related: RHEL-93425

Author: yuwata

src/resolve/resolved-dns-query.c

@@ -152,6 +152,8 @@ static int dns_query_candidate_go(DnsQueryCandidate *c) {
 
         c->query->block_ready++;
 
+        uint64_t generation = c->generation;
+
         /* Start the transactions that are not started yet */
         SET_FOREACH(t, c->transactions, i) {
                 if (t->state != DNS_TRANSACTION_NULL)
@@ -166,6 +168,13 @@ static int dns_query_candidate_go(DnsQueryCandidate *c) {
                         /* A transaction is complete. */
                         notify = true;
 
+                if (c->generation != generation)
+                        /* The transaction has been completed, and dns_transaction_complete() ->
+                         * dns_query_candidate_notify() has been already called. Moreover, the query
+                         * candidate has been regenerated, and the query should be already restarted.
+                         * Let's exit from the loop now. */
+                        return 0;
+
                 n++;
         }
 
@@ -257,6 +266,8 @@ static int dns_query_candidate_setup_transactions(DnsQueryCandidate *c) {
 
         dns_query_candidate_stop(c);
 
+        c->generation++;
+
         question = dns_query_question_for_protocol(c->query, c->scope->protocol);
 
         /* Create one transaction per question key */

src/resolve/resolved-dns-query.h

@@ -20,6 +20,7 @@ struct DnsQueryCandidate {
         DnsSearchDomain *search_domain;
 
         int error_code;
+        uint64_t generation;
         Set *transactions;
 
         LIST_FIELDS(DnsQueryCandidate, candidates_by_query);