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0d6d63e150
log_buf_pool_get_oldest_modification(): Acquire log_sys_t::flush_order_mutex in order to prevent a race condition that was introduced in commit1a6f708ec5(MDEV-15058). Before that change, log_buf_pool_get_oldest_modification() was protected by both log_sys.mutex and log_sys.flush_order_mutex like it was supposed to be ever since commita52c4820a3(MySQL 5.5.10). buf_pool_t::get_oldest_modification(): Replaces buf_pool_get_oldest_modification(), to emphasize that log_sys.flush_order_mutex must be acquired by the caller if needed. log_close(): Invoke log_buf_pool_get_oldest_modification() in order to ensure a clean shutdown. The scenario of the race condition is as follows: 1. The buffer pool is clean (no writes are pending). 2. mtr_add_dirtied_pages_to_flush_list() releases log_sys.mutex. 3. log_buf_pool_get_oldest_modification() observes that the buffer pool is clean and returns log_sys.lsn. 4. log_checkpoint() completes, writing a wrong checkpoint header according to which everything up to log_sys.lsn was clean. 5. mtr_add_dirtied_pages_to_flush_list() completes the execution of mtr_memo_note_modifications(), releases the page latches and the flush_order_mutex. 6. On a subsequent log_checkpoint(), the assertion could fail if the page modifications had not been flushed yet. The failing assertion (which is valid) was added in MySQL 5.7 mysql/mysql-server@5c6c6ec693 and merged to MariaDB Server 10.2.2 in commitfec844aca8.