MDEV-22351 InnoDB may recover wrong information after RESET MASTER

Ever since commit 947efe17
InnoDB no longer writes binlog position in one place.
It will not at all be written to the TRX_SYS page, and
instead it will be written to the undo log header page that
changes the transaction state.

trx_rseg_mem_restore(): Recover the information from the latest
written page.

storage/innobase/include/trx0sys.h

 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2020, MariaDB Corporation.
+Copyright (c) 2017, 2021, 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
@@ -857,8 +857,10 @@ class trx_sys_t
 #endif
   /** Latest recovered binlog offset */
   uint64_t recovered_binlog_offset;
-  /** Latest recovred binlog file name */
+  /** Latest recovered binlog file name */
   char recovered_binlog_filename[TRX_SYS_MYSQL_LOG_NAME_LEN];
+  /** FIL_PAGE_LSN of the page with the latest recovered binlog metadata */
+  lsn_t recovered_binlog_lsn;
 
 
   /**

storage/innobase/trx/trx0rseg.cc

 /*****************************************************************************
 
 Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2020, MariaDB Corporation.
+Copyright (c) 2017, 2021, 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
@@ -439,8 +439,14 @@ static
 void
 trx_rseg_mem_restore(trx_rseg_t* rseg, trx_id_t& max_trx_id, mtr_t* mtr)
 {
-	trx_rsegf_t*	rseg_header = trx_rsegf_get_new(
-		rseg->space->id, rseg->page_no, mtr);
+	/* This is based on trx_rsegf_get_new().
+	We need to access buf_block_t. */
+	buf_block_t *block = buf_page_get(
+		page_id_t(rseg->space->id, rseg->page_no),
+		univ_page_size, RW_S_LATCH, mtr);
+	buf_block_dbg_add_level(block, SYNC_RSEG_HEADER_NEW);
+
+	const trx_rsegf_t* rseg_header = TRX_RSEG + block->frame;
 
 	if (mach_read_from_4(rseg_header + TRX_RSEG_FORMAT) == 0) {
 		trx_id_t id = mach_read_from_8(rseg_header
@@ -451,32 +457,20 @@ trx_rseg_mem_restore(trx_rseg_t* rseg, trx_id_t& max_trx_id, mtr_t* mtr)
 		}
 
 		if (rseg_header[TRX_RSEG_BINLOG_NAME]) {
-			const char* binlog_name = reinterpret_cast<const char*>
-				(rseg_header) + TRX_RSEG_BINLOG_NAME;
+			lsn_t lsn = std::max(block->page.newest_modification,
+					     mach_read_from_8(FIL_PAGE_LSN
+							      + block->frame));
 			compile_time_assert(TRX_RSEG_BINLOG_NAME_LEN == sizeof
 					    trx_sys.recovered_binlog_filename);
-
-			int cmp = *trx_sys.recovered_binlog_filename
-				? strncmp(binlog_name,
-					  trx_sys.recovered_binlog_filename,
-					  TRX_RSEG_BINLOG_NAME_LEN)
-				: 1;
-
-			if (cmp >= 0) {
-				uint64_t binlog_offset = mach_read_from_8(
-					rseg_header + TRX_RSEG_BINLOG_OFFSET);
-				if (cmp) {
-					memcpy(trx_sys.
-					       recovered_binlog_filename,
-					       binlog_name,
-					       TRX_RSEG_BINLOG_NAME_LEN);
+			if (lsn > trx_sys.recovered_binlog_lsn) {
+				trx_sys.recovered_binlog_lsn = lsn;
 				trx_sys.recovered_binlog_offset
-						= binlog_offset;
-				} else if (binlog_offset >
-					   trx_sys.recovered_binlog_offset) {
-					trx_sys.recovered_binlog_offset
-						= binlog_offset;
-				}
+					= mach_read_from_8(
+						rseg_header
+						+ TRX_RSEG_BINLOG_OFFSET);
+				memcpy(trx_sys.recovered_binlog_filename,
+				       rseg_header + TRX_RSEG_BINLOG_NAME,
+				       TRX_RSEG_BINLOG_NAME_LEN);
 			}
 
 #ifdef WITH_WSREP