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database: clear inactive reads in stop()

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If any inactive read is left in the semaphore, it can block
`database::stop()` from shutting down, as sstables pinned by these reads
will prevent `sstables::sstables_manager::close()` from finishing. This
causes a deadlock.
It is not clear how inactive reads can be left in the semaphore, as all
users are supposed to clean up after themselves. Post 4.4 releases don't
have this problem anymore as the inactive read handle was made a RAII
object, removing the associated inactive read when destroyed. In 4.4 and
earlier release this wasn't so, so errors could be made. Normally this
is not a big issue, as these orphaned inactive reads are just evicted
when the resources they own are needed, but it does become a serious
issue during shutdown. To prevent a deadlock, clear the inactive reads
earlier, in `database::stop()` (currently they are cleared in the
destructor). This is a simple and foolproof way of ensuring any
leftover inactive reads don't cause problems.

Fixes: #8561

Tests: unit(dev)

Closes #8562
This commit is contained in:
Botond Dénes
2021-04-28 16:07:24 +03:00
committed by Avi Kivity
parent 07051f25f2
commit 840ca41393
1 changed files with 7 additions and 3 deletions
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10
database.cc
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@@ -760,9 +760,6 @@ void database::set_format_by_config() {
}
database::~database() {
_read_concurrency_sem.clear_inactive_reads();
_streaming_concurrency_sem.clear_inactive_reads();
_system_read_concurrency_sem.clear_inactive_reads();
}
void database::update_version(const utils::UUID& version) {
@@ -2016,6 +2013,13 @@ future<>
database::stop() {
assert(!_large_data_handler->running());
// Inactive reads might hold on to sstables, blocking the
// `sstables_manager::close()` calls below. No one will come back for these
// reads at this point so clear them before proceeding with the shutdown.
_read_concurrency_sem.clear_inactive_reads();
_streaming_concurrency_sem.clear_inactive_reads();
_system_read_concurrency_sem.clear_inactive_reads();
// try to ensure that CL has done disk flushing
future<> maybe_shutdown_commitlog = _commitlog != nullptr ? _commitlog->shutdown() : make_ready_future<>();
return maybe_shutdown_commitlog.then([this] {