Hi, Nirbhay! On Sep 24, Nirbhay Choubey wrote:

revision-id: 12ffe70831c9c69c3d6ef83431443696455c332b (mariadb-10.1.17-23-g12ffe70) parent(s): 8ffded0a78c0a4912b32acac4c3f58f04c3bcd87 author: Nirbhay Choubey committer: Nirbhay Choubey timestamp: 2016-09-24 00:27:38 -0400 message:

MDEV-9416: MariaDB galera got signal 11 when altering table add unique index

When a BF thread attempts to abort a victim thread's transaction, the victim thread is not locked and thus its not safe to rely on its data structures like htons registered for the trx.

So, instead of getting the registered htons from victim, innodb's hton can be looked up directly from installed_htons[] and used to abort the transaction. (Same technique is used in older versions)

diff --git a/sql/handler.cc b/sql/handler.cc index 4e4c8fa..6a32fec 100644 --- a/sql/handler.cc +++ b/sql/handler.cc @@ -6108,29 +6108,16 @@ int ha_abort_transaction(THD *bf_thd, THD *victim_thd, my_bool signal) DBUG_RETURN(0); }

- /* Try statement transaction if standard one is not set. */ - THD_TRANS *trans= (victim_thd->transaction.all.ha_list) ? - &victim_thd->transaction.all : &victim_thd->transaction.stmt; - - Ha_trx_info *ha_info= trans->ha_list, *ha_info_next; - - for (; ha_info; ha_info= ha_info_next) + handlerton *hton= installed_htons[DB_TYPE_INNODB]; + if (hton && hton->abort_transaction) { - handlerton *hton= ha_info->ht(); - if (!hton->abort_transaction) - { - /* Skip warning for binlog & wsrep. */ - if (hton->db_type != DB_TYPE_BINLOG && hton != wsrep_hton) - { - WSREP_WARN("Cannot abort transaction."); - } - } - else - { - hton->abort_transaction(hton, bf_thd, victim_thd, signal); - } - ha_info_next= ha_info->next(); + hton->abort_transaction(hton, bf_thd, victim_thd, signal);

Okay, but please add a comment that it's safe to abort from one thread (bf_thd) the transaction, running in another thread (victim_thd), because innodb's lock_sys and trx_mutex guarantee the necessary protection. And that it's not safe to access victim_thd->transaction, because it's not protected from concurrent accesses. And it's an overkill to take LOCK_plugin and iterate the whole installed_htons[] array every time. Then ok to push

} + else + { + WSREP_WARN("Cannot abort InnoDB transaction"); + } + DBUG_RETURN(0); }

Regards, Sergei Chief Architect MariaDB and security@mariadb.org