[SERVER-35217] killSessions command attempts to kill a transaction while holding SessionCatalog::_mutex, which leads to deadlock - MongoDB

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Attempting to acquire a LockManager lock while holding a mutex is prone to deadlock. The SessionCatalog::scanSessions() function locks the session catalog and executes an arbitrary function on any matching sessions. For the "killSessions" command, this means that while holding the SessionCatalog::_mutex, it calls CursorManager::killAllCursorsForTransaction(), which for a find cursor attempts to acquire the collection lock in CursorManager::withCursorManager(). Since the killAllExpiredTransactions() function also calls SessionCatalog::scanSessions(), it isn't possible to reap expired transactions while the "killSessions" command is running. It similarly isn't possible to commit or abort a transaction while the "killSessions" command is running because SessionCatalog::checkOutSession() must acquire the SessionCatalog::_mutex.

is related to

SERVER-34781 Abandoned cursor in a transaction can block other operations

SERVER-34732 collection drop hangs in test of transactions

SERVER-34795 killSessions should kill transactions prior to killing cursors

SERVER-34779 Check the dbhash periodically in a new version of the replica_sets_jscore_passthrough.yml test suite

related to

SERVER-35770 Running a multi-statement transaction when all WiredTiger write tickets are exhausted may lead to deadlock

SERVER-42550 Complete TODO listed in SERVER-35217

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