MDEV-25594: Assertion failure in DeadlockChecker::check_and_resolve()

ha_innobase::index_read(): If an autocommit non-locking transaction was
already started, refuse to access a SPATIAL INDEX.
Once a non-locking autocommit transaction has started, it must remain
in that mode (not acquire any locks).

This should fix one cause of the assertion failure that would occur in
DeadlockChecker::check_and_resolve() under heavy load, presumably
due to concurrent execution of trx_commit_in_memory().

storage/innobase/handler/ha_innodb.cc

@@ -9399,8 +9399,12 @@ ha_innobase::index_read(
 
 	/* For R-Tree index, we will always place the page lock to
 	pages being searched */
-	if (dict_index_is_spatial(index)) {
-		++m_prebuilt->trx->will_lock;
+	if (index->is_spatial() && !m_prebuilt->trx->will_lock) {
+		if (trx_is_started(m_prebuilt->trx)) {
+			DBUG_RETURN(HA_ERR_READ_ONLY_TRANSACTION);
+		} else {
+			m_prebuilt->trx->will_lock = true;
+		}
 	}
 
 	/* Note that if the index for which the search template is built is not

storage/innobase/include/dict0mem.h

@@ -2,7 +2,7 @@
 
 Copyright (c) 1996, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2012, Facebook Inc.
-Copyright (c) 2013, 2020, MariaDB Corporation.
+Copyright (c) 2013, 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
@@ -1036,6 +1036,21 @@ struct dict_index_t{
 		return DICT_CLUSTERED == (type & (DICT_CLUSTERED | DICT_IBUF));
 	}
 
+	/** @return whether this is a generated clustered index */
+	bool is_gen_clust() const { return type == DICT_CLUSTERED; }
+
+	/** @return whether this is a clustered index */
+	bool is_clust() const { return type & DICT_CLUSTERED; }
+
+	/** @return whether this is a unique index */
+	bool is_unique() const { return type & DICT_UNIQUE; }
+
+	/** @return whether this is a spatial index */
+	bool is_spatial() const { return UNIV_UNLIKELY(type & DICT_SPATIAL); }
+
+	/** @return whether this is the change buffer */
+	bool is_ibuf() const { return UNIV_UNLIKELY(type & DICT_IBUF); }
+
 	/** @return whether the index includes virtual columns */
 	bool has_virtual() const { return type & DICT_VIRTUAL; }
 
@@ -1075,9 +1090,6 @@ struct dict_index_t{
     }
   }
 
-  /** @return whether this is the change buffer */
-  bool is_ibuf() const { return UNIV_UNLIKELY(type & DICT_IBUF); }
-
   /** Assign the number of new column to be added as a part
   of the index
   @param        n_vcol  number of virtual columns to be added */