Pre-MDEV-742 InnoDB fixes

1. Refactored innobase_close_connection(). Transaction must've already
been rolled back by this time. We should expect only transactions in the
PREPARED state when MDEV-742 is done.

2. Added missing put_pins() to trx_disconnect_prepared(). Missing
put_pins() wasn't a problem because trx_disconnect_prepared() is a dead
code. But it will get revived in the main MDEV-742 patch.

3. Fixed missing reset of trx->mysql_log_file_name when RW transaction
didn't emit any log records (zero-modification RW). The problem was
detected by ASAN when disconnected XA transaction was trying to make
use of inherited mysql_log_file_name pointing into binlog data of
detached THD.

This missing reset also had user-visible side effect, when
trx_sys_print_mysql_binlog_offset() would report binlog position
not of the most recently committed transaction.

One of possible scenarios that is expected to misbehave is as following:

  thr1> CREATE TABLE t1(a INT) ENGINE=InnoDB;
  thr1> INSERT INTO t1 VALUES(1);
  thr1> BEGIN;
  thr1> UPDATE t1 SET a=1
  thr1> COMMIT; -- zero-modification, misses to reset mysql_log_file_name

  thr2> BEGIN;
  thr2> INSERT INTO t1 VALUES(2);
  thr2> COMMIT;

  thr1> BEGIN;
  thr1> do-some-real-changes;
  thr1> ROLLBACK; -- will store binlog pos from previous COMMIT in thr1?

In this case it means if binlog is replayed from position reported by
trx_sys_print_mysql_binlog_offset(), t1 will end up with two records
containing '2'.

Part of
MDEV-742 - XA PREPAREd transaction survive disconnect/server restart

storage/innobase/handler/ha_innodb.cc

@@ -4272,6 +4272,7 @@ innobase_commit_ordered_2(
 	innobase_commit_low(trx);
 
 	if (!read_only) {
+		trx->mysql_log_file_name = NULL;
 		trx->flush_log_later = false;
 
 		if (innobase_commit_concurrency > 0) {
@@ -4512,11 +4513,7 @@ innobase_rollback_trx(
 	we come here to roll back the latest SQL statement) we
 	release it now before a possibly lengthy rollback */
 	lock_unlock_table_autoinc(trx);
-
-	if (!trx->has_logged()) {
-		trx->will_lock = 0;
-		DBUG_RETURN(0);
-	}
+	trx_deregister_from_2pc(trx);
 
 	DBUG_RETURN(convert_error_code_to_mysql(trx_rollback_for_mysql(trx),
 						0, trx->mysql_thd));
@@ -4807,74 +4804,39 @@ innobase_savepoint(
 	DBUG_RETURN(convert_error_code_to_mysql(error, 0, NULL));
 }
 
-/*****************************************************************//**
-Frees a possible InnoDB trx object associated with the current THD.
-@return 0 or error number */
-static
-int
-innobase_close_connection(
-/*======================*/
-	handlerton*	hton,	/*!< in: innobase handlerton */
-	THD*		thd)	/*!< in: handle to the MySQL thread of the user
-				whose resources should be free'd */
-{
 
-	DBUG_ENTER("innobase_close_connection");
-	DBUG_ASSERT(hton == innodb_hton_ptr);
-
-	trx_t*	trx = thd_to_trx(thd);
-
-	/* During server initialization MySQL layer will try to open
-	some of the master-slave tables those residing in InnoDB.
-	After MySQL layer is done with needed checks these tables
-	are closed followed by invocation of close_connection on the
-	associated thd.
-
-	close_connection rolls back the trx and then frees it.
-	Once trx is freed thd should avoid maintaining reference to
-	it else it can be classified as stale reference.
-
-	Re-invocation of innodb_close_connection on same thd should
-	get trx as NULL. */
-
-	if (trx) {
+/**
+  Frees a possible InnoDB trx object associated with the current THD.
 
-		if (!trx_is_registered_for_2pc(trx) && trx_is_started(trx)) {
+  @param hton  innobase handlerton
+  @param thd   server thread descriptor, which resources should be free'd
 
-			sql_print_error("Transaction not registered for MariaDB 2PC, "
-				"but transaction is active");
-		}
-
-		/* Disconnect causes rollback in the following cases:
-		- trx is not started, or
-		- trx is in *not* in PREPARED state, or
-		- trx has not updated any persistent data.
-		TODO/FIXME: it does not make sense to initiate rollback
-		in the 1st and 3rd case. */
-		if (trx_is_started(trx)) {
-			if (trx_state_eq(trx, TRX_STATE_PREPARED)) {
-				if (trx->has_logged_persistent()) {
-					trx_disconnect_prepared(trx);
-				} else {
-					trx_deregister_from_2pc(trx);
-					goto rollback_and_free;
-				}
-			} else {
-			sql_print_warning(
-				"MariaDB is closing a connection that has an active "
-				"InnoDB transaction.  " TRX_ID_FMT " row modifications "
-				"will roll back.",
-					trx->undo_no);
-				goto rollback_and_free;
-			}
-		} else {
-rollback_and_free:
-			innobase_rollback_trx(trx);
-			trx_free(trx);
-		}
-	}
-
-	DBUG_RETURN(0);
+  @return 0 always
+*/
+static int innobase_close_connection(handlerton *hton, THD *thd)
+{
+  DBUG_ASSERT(hton == innodb_hton_ptr);
+  if (auto trx= thd_to_trx(thd))
+  {
+    if (trx->state == TRX_STATE_PREPARED)
+    {
+      if (trx->has_logged_persistent())
+      {
+        trx_disconnect_prepared(trx);
+        return 0;
+      }
+      innobase_rollback_trx(trx);
+    }
+    /*
+      in theory it may fire if preceding rollback failed,
+      but what can we do about it?
+    */
+    DBUG_ASSERT(!trx_is_started(trx));
+    /* some bad guy missed to reset trx->will_lock somewhere, reset it here */
+    trx->will_lock= 0;
+    trx_free(trx);
+  }
+  return 0;
 }
 
 UNIV_INTERN void lock_cancel_waiting_and_release(lock_t* lock);
@@ -17387,7 +17349,6 @@ innobase_rollback_by_xid(
 		}
 #endif /* WITH_WSREP */
 		int ret = innobase_rollback_trx(trx);
-		trx_deregister_from_2pc(trx);
 		ut_ad(!trx->will_lock);
 		trx_free(trx);
 

storage/innobase/trx/trx0trx.cc

@@ -399,6 +399,7 @@ void trx_free(trx_t*& trx)
 	ut_ad(!trx->n_mysql_tables_in_use);
 	ut_ad(!trx->mysql_n_tables_locked);
 	ut_ad(!trx->internal);
+	ut_ad(!trx->mysql_log_file_name);
 
 	if (trx->declared_to_be_inside_innodb) {
 
@@ -437,7 +438,6 @@ void trx_free(trx_t*& trx)
 
 	trx_sys.rw_trx_hash.put_pins(trx);
 	trx->mysql_thd = 0;
-	trx->mysql_log_file_name = 0;
 
 	// FIXME: We need to avoid this heap free/alloc for each commit.
 	if (trx->autoinc_locks != NULL) {
@@ -546,11 +546,13 @@ void trx_disconnect_prepared(trx_t *trx)
 {
   ut_ad(trx_state_eq(trx, TRX_STATE_PREPARED));
   ut_ad(trx->mysql_thd);
+  ut_ad(!trx->mysql_log_file_name);
   trx->read_view.close();
   trx->is_recovered= true;
   trx->mysql_thd= NULL;
   /* todo/fixme: suggest to do it at innodb prepare */
   trx->will_lock= 0;
+  trx_sys.rw_trx_hash.put_pins(trx);
 }
 
 /****************************************************************//**
@@ -1121,8 +1123,6 @@ trx_write_serialisation_history(
 	mutex_exit(&rseg->mutex);
 
 	MONITOR_INC(MONITOR_TRX_COMMIT_UNDO);
-
-	trx->mysql_log_file_name = NULL;
 }
 
 /********************************************************************