MDEV-29883 Deadlock between InnoDB statistics update and BLOB insert

This is a backport of commit 8b6a308e
from MariaDB Server 10.6.11. No attempt to reproduce the hang
in earlier an earlier version of MariaDB Server than 10.6 was made.

In each caller of fseg_n_reserved_pages() except ibuf_init_at_db_start()
which is a special case for ibuf.index at database startup, we must hold
an index latch that prevents concurrent allocation or freeing of index
pages.

Any operation that allocates or free pages that belong to an index tree
must first acquire an index latch in non-shared mode, and while
holding that, acquire an index root page latch in non-shared mode.

btr_get_size(), btr_get_size_and_reserved(): Assert that a strong enough
index latch is being held.

dict_stats_update_transient_for_index(),
dict_stats_analyze_index(): Acquire a strong enough index latch.

These operations had followed the same order of acquiring latches in
every InnoDB version since the very beginning
(commit c533308a).

The hang was introduced in
commit 2e814d47 which imported
mysql/mysql-server@ac74632293bea967b352d1b472abedeeaa921b98
which failed to strengthen the locking requirements of the function
btr_get_size().

storage/innobase/btr/btr0btr.cc

@@ -603,7 +603,7 @@ btr_get_size(
 
 	ut_ad(srv_read_only_mode
 	      || mtr_memo_contains(mtr, dict_index_get_lock(index),
-				   MTR_MEMO_S_LOCK));
+				   MTR_MEMO_SX_LOCK));
 
 	if (index->page == FIL_NULL
 	    || dict_index_is_online_ddl(index)
@@ -657,7 +657,7 @@ btr_get_size_and_reserved(
 	ulint		dummy;
 
 	ut_ad(mtr_memo_contains(mtr, dict_index_get_lock(index),
-				MTR_MEMO_S_LOCK));
+				MTR_MEMO_SX_LOCK));
 
 	ut_a(flag == BTR_N_LEAF_PAGES || flag == BTR_TOTAL_SIZE);
 

storage/innobase/dict/dict0defrag_bg.cc

 /*****************************************************************************
 
-Copyright (c) 2016, 2019, MariaDB Corporation.
+Copyright (c) 2016, 2022, 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
@@ -282,7 +282,7 @@ dict_stats_save_defrag_stats(
 	ulint	n_leaf_pages;
 	ulint	n_leaf_reserved;
 	mtr.start();
-	mtr_s_lock_index(index, &mtr);
+	mtr_sx_lock_index(index, &mtr);
 	n_leaf_reserved = btr_get_size_and_reserved(index, BTR_N_LEAF_PAGES,
 						    &n_leaf_pages, &mtr);
 	mtr.commit();

storage/innobase/dict/dict0stats.cc

 /*****************************************************************************
 
 Copyright (c) 2009, 2019, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2015, 2021, MariaDB Corporation.
+Copyright (c) 2015, 2022, 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
@@ -852,7 +852,7 @@ dict_stats_update_transient_for_index(
 		ulint	size;
 
 		mtr.start();
-		mtr_s_lock_index(index, &mtr);
+		mtr_sx_lock_index(index, &mtr);
 		size = btr_get_size(index, BTR_TOTAL_SIZE, &mtr);
 
 		if (size != ULINT_UNDEFINED) {
@@ -1945,7 +1945,7 @@ static index_stats_t dict_stats_analyze_index(dict_index_t* index)
 	DEBUG_PRINTF("  %s(index=%s)\n", __func__, index->name());
 
 	mtr.start();
-	mtr_s_lock_index(index, &mtr);
+	mtr_sx_lock_index(index, &mtr);
 	size = btr_get_size(index, BTR_TOTAL_SIZE, &mtr);
 
 	if (size != ULINT_UNDEFINED) {