MDEV-22027 Assertion oldest_lsn >= log_sys.last_checkpoint_lsn failed

log_buf_pool_get_oldest_modification(): Acquire
log_sys_t::flush_order_mutex in order to prevent a race condition
that was introduced in
commit 1a6f708ec594ac0ae2dd30db926ab07b100fa24b (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
commit a52c4820a30a69522c9876f06510662bf063bcc3 (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@5c6c6ec69336369487dfc080a6980089b4e1a3c2
and merged to MariaDB Server 10.2.2 in
commit fec844aca88e1c6b9c36bb0b811e92d9d023ffb9.

1 files changed, 3 insertions, 3 deletions

diff --git a/storage/innobase/include/log0log.h b/storage/innobase/include/log0log.h
index a2c23d0bd89..30c113dbd19 100644
--- a/storage/innobase/include/log0log.h
+++ b/storage/innobase/include/log0log.h
@@ -139,7 +139,7 @@ log_get_max_modified_age_async(void);
 /*================================*/
 
 /** Calculate the recommended highest values for lsn - last_checkpoint_lsn
-and lsn - buf_get_oldest_modification().
+and lsn - buf_pool.get_oldest_modification().
 @param[in]	file_size	requested innodb_log_file_size
 @retval true on success
 @retval false if the smallest log is too small to
@@ -667,13 +667,13 @@ public:
 	lsn_t		max_modified_age_async;
 					/*!< when this recommended
 					value for lsn -
-					buf_pool_get_oldest_modification()
+					buf_pool.get_oldest_modification()
 					is exceeded, we start an
 					asynchronous preflush of pool pages */
 	lsn_t		max_modified_age_sync;
 					/*!< when this recommended
 					value for lsn -
-					buf_pool_get_oldest_modification()
+					buf_pool.get_oldest_modification()
 					is exceeded, we start a
 					synchronous preflush of pool pages */
 	lsn_t		max_checkpoint_age_async;