fix: correct lock unlock order in Authentication classes

Fix lock order reversal in MySQL_Authentication,
ClickHouse_Authentication, and PgSQL_Authentication.

In memory_usage() and dump_all_users(), locks were acquired in order
(frontends, backends) but released in the same order instead of the
reverse. This creates a potential deadlock if another thread attempts
to acquire the same locks in opposite order.

Swap unlock calls to release backends before frontends, matching the
reverse of the acquisition order.

lib/ClickHouse_Authentication.cpp

@@ -210,11 +210,11 @@ int ClickHouse_Authentication::dump_all_users(ch_account_details_t ***ads, bool
 	*ads=_ads;
 __exit_dump_all_users:
 #ifdef PROXYSQL_AUTH_PTHREAD_MUTEX
-	pthread_rwlock_unlock(&creds_frontends.lock);
 	pthread_rwlock_unlock(&creds_backends.lock);
+	pthread_rwlock_unlock(&creds_frontends.lock);
 #else
-	spin_rdunlock(&creds_frontends.lock);
 	spin_rdunlock(&creds_backends.lock);
+	spin_rdunlock(&creds_frontends.lock);
 #endif
 	return total_size;
 }

lib/MySQL_Authentication.cpp

@@ -306,11 +306,11 @@ unsigned int MySQL_Authentication::memory_usage() {
 	ret += sizeof(PtrArray);
 	ret += (creds_backends.cred_array->size * sizeof(void *));
 #ifdef PROXYSQL_AUTH_PTHREAD_MUTEX
-	pthread_rwlock_unlock(&creds_frontends.lock);
 	pthread_rwlock_unlock(&creds_backends.lock);
+	pthread_rwlock_unlock(&creds_frontends.lock);
 #else
-	spin_rdunlock(&creds_frontends.lock);
 	spin_rdunlock(&creds_backends.lock);
+	spin_rdunlock(&creds_frontends.lock);
 #endif
 	return ret;
 }
@@ -392,11 +392,11 @@ int MySQL_Authentication::dump_all_users(account_details_t ***ads, bool _complet
 	*ads=_ads;
 __exit_dump_all_users:
 #ifdef PROXYSQL_AUTH_PTHREAD_MUTEX
-	pthread_rwlock_unlock(&creds_frontends.lock);
 	pthread_rwlock_unlock(&creds_backends.lock);
+	pthread_rwlock_unlock(&creds_frontends.lock);
 #else
-	spin_rdunlock(&creds_frontends.lock);
 	spin_rdunlock(&creds_backends.lock);
+	spin_rdunlock(&creds_frontends.lock);
 #endif
 	return total_size;
 }

lib/PgSQL_Authentication.cpp

@@ -250,11 +250,11 @@ unsigned int PgSQL_Authentication::memory_usage() {
 	ret += sizeof(PtrArray);
 	ret += (creds_backends.cred_array->size * sizeof(void *));
 #ifdef PROXYSQL_AUTH_PTHREAD_MUTEX
-	pthread_rwlock_unlock(&creds_frontends.lock);
 	pthread_rwlock_unlock(&creds_backends.lock);
+	pthread_rwlock_unlock(&creds_frontends.lock);
 #else
-	spin_rdunlock(&creds_frontends.lock);
 	spin_rdunlock(&creds_backends.lock);
+	spin_rdunlock(&creds_frontends.lock);
 #endif
 	return ret;
 }
@@ -327,11 +327,11 @@ int PgSQL_Authentication::dump_all_users(pgsql_account_details_t***ads, bool _co
 	*ads=_ads;
 __exit_dump_all_users:
 #ifdef PROXYSQL_AUTH_PTHREAD_MUTEX
-	pthread_rwlock_unlock(&creds_frontends.lock);
 	pthread_rwlock_unlock(&creds_backends.lock);
+	pthread_rwlock_unlock(&creds_frontends.lock);
 #else
-	spin_rdunlock(&creds_frontends.lock);
 	spin_rdunlock(&creds_backends.lock);
+	spin_rdunlock(&creds_frontends.lock);
 #endif
 	return total_size;
 }