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Kernel: Disable interrupts while setting up a thread blocker

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There was a race window between instantiating a WaitQueueBlocker and
setting the thread state to Blocked. If a thread was preempted between
those steps, someone else might try to wake the wait queue and find an
unblocked thread in a wait queue, which is not sane.
This commit is contained in:
Andreas Kling 2019-12-01 12:45:51 +01:00
parent f067730f6b
commit 9ed272ce98
2 changed files with 24 additions and 3 deletions
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12
Kernel/Thread.h
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@ -274,11 +274,17 @@ public:
ASSERT(state() == Thread::Running);
ASSERT(m_blocker == nullptr);
T t(AK::forward<Args>(args)...);
// NOTE: We disable interrupts here to avoid the situation where a WaitQueueBlocker
// adds the current thread to a WaitQueue, and then someone wakes up before
// we set the state to Blocked decides to wake the queue. They would find
// unblocked threads in a wait queue, which would not be good. We can't go
// into Blocked state earlier, since that would prevent this thread from
// getting scheduled.
auto saved_if = cli_and_save_interrupt_flag();
T t(forward<Args>(args)...);
m_blocker = &t;
// Enter blocked state.
set_state(Thread::Blocked);
restore_interrupt_flag(saved_if);
// Yield to the scheduler, and wait for us to resume unblocked.
if (beneficiary) {