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3cb081eb84
" Fix races that may lead to use-after-free events and file system level exceptions during shutdown and drain. The root cause of use-after-free events in question is that space_watchdog blocks on end_point_hints_manager::file_update_mutex() and we need to make sure this mutex is alive as long as it's accessed even if the corresponding end_point_hints_manager instance is destroyed in the context of manager::drain_for(). File system exceptions may occur when space_watchdog attempts to scan a directory while it's being deleted from the drain_for() context. In case of such an exception new hints generation is going to be blocked - including for materialized views, till the next space_watchdog round (in 1s). Issues that are fixed are #4685 and #4836. Tested as follows: 1) Patched the code in order to trigger the race with (a lot) higher probability and running slightly modified hinted handoff replace dtest with a debug binary for 100 times. Side effect of this testing was discovering of #4836. 2) Using the same patch as above tested that there are no crashes and nodes survive stop/start sequences (they were not without this series) in the context of all hinted handoff dtests. Ran the whole set of tests with dev binary for 10 times. " * 'hinted_handoff_race_between_drain_for_and_space_watchdog_no_global_lock-v2' of https://github.com/vladzcloudius/scylla: hinted handoff: fix a race on a directory removal between space_watchdog and drain_for() hinted handoff: make taking file_update_mutex safe db::hints::manager::drain_for(): fix alignment db::hints::manager: serialize calls to drain_for() db::hints: cosmetics: identation and missing method qualifier