MDEV-26631 InnoDB fails to fetch page from doublewrite buffer

Problem:
========
InnoDB fails to fetch the page0 from dblwr if page0 is
corrupted.In that case, InnoDB defers the tablespace
and doesn't find the INIT_PAGE redo log record for page0
and it leads to failure.

Solution:
=========
 InnoDB should recover page0 from dblwr if space_id can
be found for deferred tablespace.

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

@@ -65,6 +65,7 @@ where name = 'test/t1';
 # Ensure that dirty pages of table t1 is flushed.
 flush tables t1 for export;
 unlock tables;
+set global innodb_log_checkpoint_now=1;
 begin;
 insert into t1 values (6, repeat('%', 12));
 # Make the first page dirty for table t1

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

@@ -159,6 +159,8 @@ where name = 'test/t1';
 flush tables t1 for export;
 unlock tables;
 
+set global innodb_log_checkpoint_now=1;
+
 begin;
 insert into t1 values (6, repeat('%', 12));
 

storage/innobase/fsp/fsp0file.cc

@@ -400,10 +400,19 @@ Datafile::validate_for_recovery()
 	err = validate_first_page(0);
 
 	switch (err) {
-	case DB_SUCCESS:
 	case DB_TABLESPACE_EXISTS:
 		break;
-
+	case DB_SUCCESS:
+		if (!m_defer || !m_space_id) {
+			break;
+		}
+		/* InnoDB should check whether the deferred
+		tablespace page0 can be recovered from
+		double write buffer. InnoDB should try
+	        to recover only if m_space_id exists because
+		dblwr pages can be searched via {space_id, 0}.
+		m_space_id is set in read_first_page(). */
+		/* fall through */
 	default:
 		/* Re-open the file in read-write mode  Attempt to restore
 		page 0 from doublewrite and read the space ID from a survey
@@ -414,23 +423,30 @@ Datafile::validate_for_recovery()
 			return(err);
 		}
 
+		if (!m_defer) {
 			err = find_space_id();
 			if (err != DB_SUCCESS || m_space_id == 0) {
-			ib::error() << "Datafile '" << m_filepath << "' is"
-				" corrupted. Cannot determine the space ID from"
-				" the first 64 pages.";
+				ib::error() << "Datafile '" << m_filepath
+					<< "' is corrupted. Cannot determine "
+					"the space ID from the first 64 pages.";
 				return(err);
 			}
+		}
+
 		if (m_space_id == ULINT_UNDEFINED) {
 			return DB_SUCCESS; /* empty file */
 		}
 
 		if (restore_from_doublewrite()) {
+			if (m_defer) {
+				return err;
+			}
 			return(DB_CORRUPTION);
 		}
 
 		/* Free the previously read first page and then re-validate. */
 		free_first_page();
+		m_defer = false;
 		err = validate_first_page(0);
 	}