Race conditions in SHOW ENGINE INNODB MUTEX

The function innodb_show_mutex_status() is the only ultimate caller of LatchCounter::iterate() via MutexMonitor::iterate(). Because the call is not protected by LatchCounter::m_mutex, any mutex_create() or mutex_free() that is invoked concurrently during the execution, bad things such as a crash could happen.

I think that the most likely way for this to happen is buffer pool resizing, which could cause buf_block_t::mutex (which existed before MDEV-15053) to be created or freed. We could also register InnoDB mutexes in TrxFactory::init() if trx_pools needs to grow.

The view INFORMATION_SCHEMA.INNODB_MUTEXES is not affected, because it only displays information about rw-locks, not mutexes.