Temp table in the crashing thread is belongs to Thread 77. This should be enough for a DEBUG_SYNC testcase and fix. Not a duplicate of bug 1193308, but indeed similar.

Thread 77 (Thread 0x7fe73f535700 (LWP 12875)):
+bt
#0  0x00007fe758901c0d in fsync () from /lib64/libpthread.so.0
#1  0x000000000093958d in os_file_fsync (file=131) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/os/os0file.cc:2285
#2  0x0000000000939639 in os_file_flush_func (file=<optimized out>) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/os/os0file.cc:2386
#3  0x0000000000a383a4 in pfs_os_file_flush_func (file=131, src_line=3440, src_file=0xc013f0 "/bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/fil/fil0fil.cc") at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/include/os0file.ic:355
#4  0x0000000000a43cf0 in fil_create_new_single_table_tablespace (space_id=69, tablename=0x7fe6c40089c0 "query112928/#sql-ib70", dir_path=<optimized out>, flags=0, flags2=<optimized out>, size=4) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/fil/fil0fil.cc:3440
#5  0x0000000000a15ba3 in dict_build_table_def_step (thr=0x7fe6c40224e0, node=0x7fe6c403bc68) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/dict/dict0crea.cc:306
#6  0x0000000000a161db in dict_create_table_step (thr=0x7fe6c40224e0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/dict/dict0crea.cc:1030
#7  0x000000000095acdd in que_thr_step (thr=0x7fe6c40224e0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/que/que0que.cc:1123
#8  que_run_threads_low (thr=0x7fe6c40224e0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/que/que0que.cc:1177
#9  que_run_threads (thr=0x7fe6c40224e0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/que/que0que.cc:1218
#10 0x000000000098357c in row_create_table_for_mysql (table=0x7fe6c40107a8, trx=0x7fe6c4020bb0, commit=false) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/row/row0mysql.cc:2263
#11 0x00000000008fe413 in prepare_inplace_alter_table_dict (ha_alter_info=0x7fe73f532ca0, altered_table=0x7fe6c4010ae0, old_table=0x7fe62800e390, table_name=0x7fe62800834c "t1", flags=1, flags2=16, fts_doc_id_col=18446744073709551615, add_fts_doc_id=false, add_fts_doc_id_idx=<optimized out>) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/handler/handler0alter.cc:2812
#12 0x000000000090031f in ha_innobase::prepare_inplace_alter_table (this=<optimized out>, altered_table=<optimized out>, ha_alter_info=<optimized out>) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/innobase/handler/handler0alter.cc:3821
#13 0x0000000000b09e1a in ha_partition::prepare_inplace_alter_table (this=0x7fe62800ec80, altered_table=0x7fe6c4010ae0, ha_alter_info=0x7fe73f532ca0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/ha_partition.cc:7950
#14 0x000000000072eba5 in mysql_inplace_alter_table (thd=0x1c609f0, table_list=0x7fe628004da0, table=0x7fe62800e390, altered_table=0x7fe6c4010ae0, ha_alter_info=0x7fe73f532ca0, inplace_supported=HA_ALTER_INPLACE_NO_LOCK_AFTER_PREPARE, target_mdl_request=0x7fe73f532a10, alter_ctx=0x7fe73f5313f0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/sql_table.cc:6469
#15 0x0000000000731007 in mysql_alter_table (thd=<optimized out>, new_db=0x7fe73f533410 "", new_name=<optimized out>, create_info=<optimized out>, table_list=0x7fe628004da0, alter_info=<optimized out>, order_num=0, order=0x0, ignore=false) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/sql_table.cc:8369
#16 0x0000000000818977 in Sql_cmd_alter_table::execute (this=<optimized out>, thd=0x1c609f0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/sql_alter.cc:317
#17 0x00000000006de1d0 in mysql_execute_command (thd=0x1c609f0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/sql_parse.cc:5132
#18 0x00000000006e1588 in mysql_parse (thd=0x1c609f0, rawbuf=<optimized out>, length=29764984, parser_state=<optimized out>) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/sql_parse.cc:6451
#19 0x00000000006e2441 in dispatch_command (command=COM_QUERY, thd=0x1c609f0, packet=0x1c6d431 "ALTER TABLE query112928 . `t1` DROP COLUMN `c17`", packet_length=48) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/sql_parse.cc:1376
#20 0x000000000077ba2f in threadpool_process_request (thd=0x1c609f0) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/threadpool_common.cc:312
#21 0x000000000077ddd8 in handle_event (connection=0x1c44850) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/threadpool_unix.cc:1466
#22 worker_main (param=0x12dfa00 <all_groups+7680>) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/sql/threadpool_unix.cc:1519
#23 0x0000000000ab05d9 in pfs_spawn_thread (arg=0x1c53110) at /bzr/5.6_opt/Percona-Server-5.6.11-rc60.3/storage/perfschema/pfs.cc:1853
#24 0x00007fe7588fa851 in start_thread () from /lib64/libpthread.so.0
#25 0x00007fe75706d90d in clone () from /lib64/libc.so.6