Starting with commit da094188 (MDEV-24393),
MariaDB will no longer acquire advisory file locks on InnoDB data
files by default, because it would create a large number of
entries in Linux /proc/locks.

The motivation for acquiring the file locks is to prevent accidental
concurrent startup of multiple server processes on the same data files.
Such mistake still turns out to be relatively common, based on
corruption bug reports from the community.

To prevent corruption due to concurrent startup attempts, the
Aria storage engine would unconditionally acquire an advisory lock
on one of its log files.

Solution: InnoDB will always lock its system tablespace files.
(Ever since commit 685d958e
the InnoDB log file will not necessarily be open while the
server is running, because it can be accessed via memory-mapped I/O.)

If more protection is desired, then the option --external-locking
can be used.

The mandatory advisory lock also fixes intermittent failures of
some crash recovery tests. It turns out that when the mtr test harness
kills and restarts the server, it will not actually ensure that the
old process has terminated before starting the new one.