BUG#18942294 - SEGV IN DICT_FIND_TABLE_BY_SPACE TRYING TO MARK SPACE CORRUPT

IN RECOVERY

During redo log processing, the data dictionary is not available. We should
check it in dict_find_table_by_space() to prevent SEGV error.

rb#5678, approved by Jimmy.

storage/innobase/buf/buf0buf.c

@@ -3562,6 +3562,10 @@ buf_page_io_complete(
 				(ulong) bpage->offset);
 		}
 
+		DBUG_EXECUTE_IF("set_dict_sys_to_null",
+				dict_sys = NULL;
+				goto corrupt;);
+
 		/* From version 3.23.38 up we store the page checksum
 		to the 4 first bytes of the page end lsn field */
 
@@ -3616,6 +3620,11 @@ buf_page_io_complete(
 					      " because of"
 					      " a corrupt database page.\n",
 					      stderr);
+
+					DBUG_EXECUTE_IF(
+						"set_dict_sys_to_null",
+						DBUG_SUICIDE(););
+
 					ut_error;
 				}
 			}

storage/innobase/dict/dict0dict.c

@@ -5364,6 +5364,11 @@ dict_find_table_by_space(
 
 	ut_ad(space_id > 0);
 
+	if (dict_sys == NULL) {
+		/* This could happen when it's in redo processing. */
+		return(NULL);
+	}
+
 	table = UT_LIST_GET_FIRST(dict_sys->table_LRU);
 	num_item =  UT_LIST_GET_LEN(dict_sys->table_LRU);