MDEV-14988 innodb_read_only tries to modify files if transactions were recovered in COMMITTED state

lock_trx_release_locks(): Relax a debug assertion to allow
recovered TRX_STATE_COMMITTED_IN_MEMORY transactions.

trx_commit_in_memory(): Add DEBUG_SYNC instrumentation.

trx_undo_insert_cleanup(): Skip persistent changes if innodb_read_only
is set. This should only happen when a recovered committed transaction
would be cleaned up at shutdown.

mysql-test/suite/innodb/r/read_only_recover_committed.result

@@ -0,0 +1,43 @@
+CREATE TABLE t(a INT PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t VALUES(1);
+BEGIN;
+INSERT INTO t VALUES(2);
+DELETE FROM t WHERE a=2;
+# Normal MariaDB shutdown would roll back the above transaction.
+# We want the transaction to remain open, so we will kill the server
+# after ensuring that any non-transactional files are clean.
+FLUSH TABLES;
+# Create another transaction that will be recovered as COMMITTED.
+BEGIN;
+SET DEBUG_SYNC='after_trx_committed_in_memory SIGNAL committed WAIT_FOR ever';
+COMMIT;
+SET DEBUG_SYNC='now WAIT_FOR committed';
+# Ensure that the above incomplete transactions become durable.
+SET GLOBAL innodb_flush_log_at_trx_commit=1;
+BEGIN;
+INSERT INTO t VALUES(-10000);
+ROLLBACK;
+SELECT * FROM t;
+a
+1
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+SELECT * FROM t;
+a
+1
+UPDATE t SET a=3 WHERE a=1;
+ERROR HY000: Table 't' is read only
+# Starting with MariaDB 10.2, innodb_read_only implies READ UNCOMMITTED.
+# In earlier versions, this would return the last committed version
+# (empty table)!
+SELECT * FROM t;
+a
+1
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+SELECT * FROM t;
+a
+1
+SELECT * FROM t;
+a
+1
+DROP TABLE t;
+NOT FOUND /Rolled back recovered transaction [^0]/ in mysqld.1.err

mysql-test/suite/innodb/t/read_only_recover_committed.test

@@ -0,0 +1,68 @@
+--source include/have_innodb.inc
+--source include/have_debug.inc
+--source include/have_debug_sync.inc
+# need to restart server
+--source include/not_embedded.inc
+
+--connect(con1, localhost, root)
+CREATE TABLE t(a INT PRIMARY KEY) ENGINE=InnoDB;
+INSERT INTO t VALUES(1);
+BEGIN;
+# Generate insert_undo log.
+INSERT INTO t VALUES(2);
+# Generate update_undo log.
+DELETE FROM t WHERE a=2;
+--connect(con2, localhost, root)
+--echo # Normal MariaDB shutdown would roll back the above transaction.
+--echo # We want the transaction to remain open, so we will kill the server
+--echo # after ensuring that any non-transactional files are clean.
+FLUSH TABLES;
+--echo # Create another transaction that will be recovered as COMMITTED.
+BEGIN;
+# Generate multiple pages of both insert_undo and update_undo, so that
+# the state TRX_UNDO_CACHE will not be chosen.
+--disable_query_log
+let $n= 10000;
+while ($n) {
+dec $n;
+eval INSERT INTO t VALUES(-$n);
+eval DELETE FROM t WHERE a=-$n;
+}
+--enable_query_log
+SET DEBUG_SYNC='after_trx_committed_in_memory SIGNAL committed WAIT_FOR ever';
+send COMMIT;
+
+connection default;
+SET DEBUG_SYNC='now WAIT_FOR committed';
+--echo # Ensure that the above incomplete transactions become durable.
+SET GLOBAL innodb_flush_log_at_trx_commit=1;
+BEGIN;
+INSERT INTO t VALUES(-10000);
+ROLLBACK;
+--let $restart_parameters= --innodb-force-recovery=3
+--let $shutdown_timeout= 0
+--source include/restart_mysqld.inc
+--let $shutdown_timeout= 30
+--disconnect con1
+--disconnect con2
+SELECT * FROM t;
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+SELECT * FROM t;
+# refused on MySQL 5.6, MariaDB 10.0, 10.1, but not MariaDB 10.2+
+--error ER_OPEN_AS_READONLY
+UPDATE t SET a=3 WHERE a=1;
+--let $restart_parameters= --innodb-read-only
+--source include/restart_mysqld.inc
+--echo # Starting with MariaDB 10.2, innodb_read_only implies READ UNCOMMITTED.
+--echo # In earlier versions, this would return the last committed version
+--echo # (empty table)!
+SELECT * FROM t;
+SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
+SELECT * FROM t;
+--let $restart_parameters=
+--source include/restart_mysqld.inc
+SELECT * FROM t;
+DROP TABLE t;
+let SEARCH_FILE= $MYSQLTEST_VARDIR/log/mysqld.1.err;
+--let SEARCH_PATTERN= Rolled back recovered transaction [^0]
+--source include/search_pattern_in_file.inc

storage/innobase/lock/lock0lock.cc

@@ -7000,7 +7000,10 @@ lock_trx_release_locks(
 		}
 		mutex_exit(&trx_sys->mutex);
 	} else {
-		ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE));
+		ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE)
+		      || (trx_state_eq(trx, TRX_STATE_COMMITTED_IN_MEMORY)
+			  && trx->is_recovered
+			  && !UT_LIST_GET_LEN(trx->lock.trx_locks)));
 	}
 
 	/* The transition of trx->state to TRX_STATE_COMMITTED_IN_MEMORY

storage/innobase/trx/trx0trx.cc

@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, MariaDB Corporation.
+Copyright (c) 2017, 2018, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -1227,6 +1227,8 @@ trx_commit_in_memory(
 	trx->read_view = NULL;
 
 	if (lsn) {
+		DEBUG_SYNC_C("after_trx_committed_in_memory");
+
 		if (trx->insert_undo != NULL) {
 
 			trx_undo_insert_cleanup(trx);

storage/innobase/trx/trx0undo.cc

@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2014, 2017, MariaDB Corporation.
+Copyright (c) 2014, 2018, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -1989,7 +1989,9 @@ trx_undo_insert_cleanup(
 
 		mutex_exit(&(rseg->mutex));
 
-		trx_undo_seg_free(undo);
+		if (!srv_read_only_mode) {
+			trx_undo_seg_free(undo);
+		}
 
 		mutex_enter(&(rseg->mutex));
 

storage/xtradb/lock/lock0lock.cc

@@ -7099,7 +7099,10 @@ lock_trx_release_locks(
 		}
 		mutex_exit(&trx_sys->mutex);
 	} else {
-		ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE));
+		ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE)
+		      || (trx_state_eq(trx, TRX_STATE_COMMITTED_IN_MEMORY)
+			  && trx->is_recovered
+			  && !UT_LIST_GET_LEN(trx->lock.trx_locks)));
 	}
 
 	/* The transition of trx->state to TRX_STATE_COMMITTED_IN_MEMORY

storage/xtradb/trx/trx0trx.cc

@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, MariaDB Corporation.
+Copyright (c) 2017, 2018, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -1442,6 +1442,8 @@ trx_commit_in_memory(
 	if (lsn) {
 		ulint	flush_log_at_trx_commit;
 
+		DEBUG_SYNC_C("after_trx_committed_in_memory");
+
 		if (trx->insert_undo != NULL) {
 
 			trx_undo_insert_cleanup(trx);

storage/xtradb/trx/trx0undo.cc

@@ -1,7 +1,7 @@
 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2014, 2017, MariaDB Corporation.
+Copyright (c) 2014, 2018, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -1989,7 +1989,9 @@ trx_undo_insert_cleanup(
 
 		mutex_exit(&(rseg->mutex));
 
-		trx_undo_seg_free(undo);
+		if (!srv_read_only_mode) {
+			trx_undo_seg_free(undo);
+		}
 
 		mutex_enter(&(rseg->mutex));