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MDEV-23536 : Race condition between KILL and transaction commit
A race condition may occur between the execution of transaction commit, and an execution of a KILL statement that would attempt to abort that transaction. MDEV-17092 worked around this race condition by modifying InnoDB code. After that issue was closed, Sergey Vojtovich pointed out that this race condition would better be fixed above the storage engine layer: If you look carefully into the above, you can conclude that thd->free_connection() can be called concurrently with KILL/thd->awake(). Which is the bug. And it is partially fixed in THD::~THD(), that is destructor waits for KILL completion: Fix: Add necessary mutex operations to THD::free_connection() and move WSREP specific code also there. This ensures that no one is using THD while we do free_connection(). These mutexes will also ensures that there can't be concurrent KILL/THD::awake(). innobase_kill_query We can now remove usage of trx_sys_mutex introduced on MDEV-17092. trx_t::free() Poison trx->state and trx->mysql_thd This patch is validated with an RQG run similar to the one that reproduced MDEV-17092.
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Jan Lindström
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Jan 8, 2021
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