btr0cur.h, btr0btr.h, btr0btr.c, btr0cur.c, row0purge.c:

  Fix a hang associated with an index tree of height 1 and purging of BLOB fields from it


innobase/row/row0purge.c:
  Fix a hang associated with an index tree of height 1 and purging of BLOB fields from it
innobase/btr/btr0cur.c:
  Fix a hang associated with an index tree of height 1 and purging of BLOB fields from it
innobase/btr/btr0btr.c:
  Fix a hang associated with an index tree of height 1 and purging of BLOB fields from it
innobase/include/btr0btr.h:
  Fix a hang associated with an index tree of height 1 and purging of BLOB fields from it
innobase/include/btr0cur.h:
  Fix a hang associated with an index tree of height 1 and purging of BLOB fields from it

innobase/btr/btr0btr.c

@@ -135,7 +135,7 @@ btr_page_insert_fits(
 
 /******************************************************************
 Gets the root node of a tree and x-latches it. */
-static
+
 page_t*
 btr_root_get(
 /*=========*/
@@ -146,9 +146,6 @@ btr_root_get(
 	ulint	space;
 	ulint	root_page_no;
 	page_t*	root;
-
-	ut_ad(mtr_memo_contains(mtr, dict_tree_get_lock(tree), MTR_MEMO_X_LOCK)
-	  || mtr_memo_contains(mtr, dict_tree_get_lock(tree), MTR_MEMO_S_LOCK));
 	
 	space = dict_tree_get_space(tree);
 	root_page_no = dict_tree_get_page(tree);
@@ -334,8 +331,6 @@ btr_page_alloc(
 	page_t*		new_page;
 	ulint		new_page_no;
 
-	ut_ad(mtr_memo_contains(mtr, dict_tree_get_lock(tree),
-							MTR_MEMO_X_LOCK));
 	if (tree->type & DICT_IBUF) {
 
 		return(btr_page_alloc_for_ibuf(tree, mtr));

innobase/btr/btr0cur.c

@@ -3180,7 +3180,7 @@ btr_store_big_rec_extern_fields(
 
 	ut_ad(mtr_memo_contains(local_mtr, dict_tree_get_lock(index->tree),
 							MTR_MEMO_X_LOCK));
-	ut_ad(mtr_memo_contains(local_mtr, buf_block_align(data),
+	ut_ad(mtr_memo_contains(local_mtr, buf_block_align(rec),
 							MTR_MEMO_PAGE_X_FIX));	
 	ut_a(index->type & DICT_CLUSTERED);
 							
@@ -3315,7 +3315,13 @@ void
 btr_free_externally_stored_field(
 /*=============================*/
 	dict_index_t*	index,		/* in: index of the data, the index
-					tree MUST be X-latched */
+					tree MUST be X-latched; if the tree
+					height is 1, then also the root page
+					must be X-latched! (this is relevant
+					in the case this function is called
+					from purge where 'data' is located on
+					an undo log page, not an index
+					page) */
 	byte*		data,		/* in: internally stored data
 					+ reference to the externally
 					stored part */

innobase/include/btr0btr.h

@@ -55,6 +55,15 @@ UNIQUE definition on secondary indexes when we decide if we can use the
 insert buffer to speed up inserts */
 #define BTR_IGNORE_SEC_UNIQUE	2048	
 
+/******************************************************************
+Gets the root node of a tree and x-latches it. */
+
+page_t*
+btr_root_get(
+/*=========*/
+				/* out: root page, x-latched */
+	dict_tree_t*	tree,	/* in: index tree */
+	mtr_t*		mtr);	/* in: mtr */
 /******************************************************************
 Gets a buffer page and declares its latching order level. */
 UNIV_INLINE

innobase/include/btr0cur.h

@@ -507,7 +507,13 @@ void
 btr_free_externally_stored_field(
 /*=============================*/
 	dict_index_t*	index,		/* in: index of the data, the index
-					tree MUST be X-latched */
+					tree MUST be X-latched; if the tree
+					height is 1, then also the root page
+					must be X-latched! (this is relevant
+					in the case this function is called
+					from purge where 'data' is located on
+					an undo log page, not an index
+					page) */
 	byte*		data,		/* in: internally stored data
 					+ reference to the externally
 					stored part */

innobase/row/row0purge.c

@@ -429,7 +429,18 @@ row_purge_upd_exist_or_extern(
 			index = dict_table_get_first_index(node->table);
 
 			mtr_x_lock(dict_tree_get_lock(index->tree), &mtr);
+
+			/* NOTE: we must also acquire an X-latch to the
+			root page of the tree. We will need it when we
+			free pages from the tree. If the tree is of height 1,
+			the tree X-latch does NOT protect the root page,
+			because it is also a leaf page. Since we will have a
+			latch on an undo log page, we would break the
+			latching order if we would only later latch the
+			root page of such a tree! */
 			
+			btr_root_get(index->tree, &mtr);
+
 			/* We assume in purge of externally stored fields
 			that the space id of the undo log record is 0! */