MDEV-19614 SET GLOBAL innodb_ deadlock due to LOCK_global_system_variables
The update callback functions for several settable global InnoDB variables are acquiring InnoDB latches while holding LOCK_global_system_variables. On the other hand, some InnoDB code is invoking THDVAR() while holding InnoDB latches. An example of this is thd_lock_wait_timeout() that is called by lock_rec_enqueue_waiting(). In some cases, the intern_sys_var_ptr() that is invoked by THDVAR() may acquire LOCK_global_system_variables, via sync_dynamic_session_variables(). In lock_rec_enqueue_waiting(), we really must be holding some InnoDB latch while invoking THDVAR(). This implies that LOCK_global_system_variables must conceptually reside below any InnoDB latch in the latching order. That in turns implies that the various update callback functions must release LOCK_global_system_variables before acquiring any InnoDB mutexes or rw-locks, and reacquire LOCK_global_system_variables later. The validate functions are being invoked while not holding LOCK_global_system_variables and thus they do not need any changes. The following statements are affected by this: SET GLOBAL innodb_adaptive_hash_index = …; SET GLOBAL innodb_cmp_per_index_enabled = 1; SET GLOBAL innodb_old_blocks_pct = …; SET GLOBAL innodb_fil_make_page_dirty_debug = …; -- debug builds only SET GLOBAL innodb_buffer_pool_evict = uncompressed; -- debug builds only SET GLOBAL innodb_purge_run_now = 1; -- debug builds only SET GLOBAL innodb_purge_stop_now = 1; -- debug builds only SET GLOBAL innodb_log_checkpoint_now = 1; -- debug builds only SET GLOBAL innodb_buf_flush_list_now = 1; -- debug builds only SET GLOBAL innodb_buffer_pool_dump_now = 1; SET GLOBAL innodb_buffer_pool_load_now = 1; SET GLOBAL innodb_buffer_pool_load_abort = 1; SET GLOBAL innodb_status_output = …; SET GLOBAL innodb_status_output_locks = …; SET GLOBAL innodb_encryption_threads = …; SET GLOBAL innodb_encryption_rotate_key_age = …; SET GLOBAL innodb_encryption_rotation_iops = …; SET GLOBAL innodb_encrypt_tables = …; SET GLOBAL innodb_disallow_writes = …; buf_LRU_old_ratio_update(): Correct the return type.
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