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Kernel: Enhance WaitQueue to remember pending wakes

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If WaitQueue::wake_all, WaitQueue::wake_one, or WaitQueue::wake_n
is called but nobody is currently waiting, we should remember that
fact and prevent someone from waiting after such a request. This
solves a race condition where the Finalizer thread is notified
to finalize a thread, but it is not (yet) waiting on this queue.

Fixes #2693
This commit is contained in:
Tom 2020-07-05 15:46:51 -06:00 • committed by Andreas Kling
parent 2a82a25fec
commit 9725bda63e
5 changed files with 93 additions and 27 deletions
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28
Kernel/Lock.cpp
View file

@ -54,20 +54,20 @@ void Lock::lock(Mode mode)
for (;;) {
bool expected = false;
if (m_lock.compare_exchange_strong(expected, true, AK::memory_order_acq_rel)) {
// FIXME: Do not add new readers if writers are queued.
bool modes_dont_conflict = !modes_conflict(m_mode, mode);
bool already_hold_exclusive_lock = m_mode == Mode::Exclusive && m_holder == current_thread;
if (modes_dont_conflict || already_hold_exclusive_lock) {
// We got the lock!
if (!already_hold_exclusive_lock)
m_mode = mode;
m_holder = current_thread;
m_times_locked++;
m_lock.store(false, AK::memory_order_release);
return;
}
timeval* timeout = nullptr;
current_thread->wait_on(m_queue, m_name, timeout, &m_lock, m_holder);
do {
// FIXME: Do not add new readers if writers are queued.
bool modes_dont_conflict = !modes_conflict(m_mode, mode);
bool already_hold_exclusive_lock = m_mode == Mode::Exclusive && m_holder == current_thread;
if (modes_dont_conflict || already_hold_exclusive_lock) {
// We got the lock!
if (!already_hold_exclusive_lock)
m_mode = mode;
m_holder = current_thread;
m_times_locked++;
m_lock.store(false, AK::memory_order_release);
return;
}
} while (current_thread->wait_on(m_queue, m_name, nullptr, &m_lock, m_holder) == Thread::BlockResult::NotBlocked);
} else if (Processor::current().in_critical()) {
// If we're in a critical section and trying to lock, no context
// switch will happen, so yield.