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There is a race condition related to the variable srv_stats.n_lock_wait_current_count, which is only incremented and decremented by the function lock_wait_suspend_thread(), The incrementing is protected by lock_sys->wait_mutex, but the decrementing does not appear to be protected by anything. This mismatch could allow the counter to be corrupted when a transactional InnoDB table or record lock wait is terminating roughly at the same time with the start of a wait on a (possibly different) lock. ib_counter_t: Remove some unused methods. Prevent instantiation for N=1. Add an inc() method that takes a slot index as a parameter. single_indexer_t: Remove. simple_counter<typename Type, bool atomic=false>: A new counter wrapper. Optionally use atomic memory operations for modifying the counter. Aligned to the cache line size. lsn_ctr_1_t, ulint_ctr_1_t, int64_ctr_1_t: Define as simple_counter<Type>. These counters are either only incremented (and we do not care about losing some increment operations), or the increment/decrement operations are protected by some mutex. srv_stats_t::os_log_pending_writes: Document that the number is protected by log_sys->mutex. srv_stats_t::n_lock_wait_current_count: Use simple_counter<ulint, true>, that is, atomic inc() and dec() operations. lock_wait_suspend_thread(): Release the mutexes before incrementing the counters. Avoid acquiring the lock mutex if the lock wait has already been resolved. Atomically increment and decrement srv_stats.n_lock_wait_current_count. row_insert_for_mysql(), row_update_for_mysql(), row_update_cascade_for_mysql(): Use the inc() method with the trx->id as the slot index. This is a non-functional change, just using inc() instead of add(1). buf_LRU_get_free_block(): Replace the method add(index, n) with inc(). There is no slot index in the simple_counter. |
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| lock0iter.cc | ||
| lock0lock.cc | ||
| lock0wait.cc | ||