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Kernel: Fix some race conditions with Lock and waiting/waking threads

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There is a window between acquiring/releasing the lock with the atomic
variables and subsequently waiting or waking threads. With a single
processor this window was closed by using a critical section, but
this doesn't prevent other processors from running these code paths.
To solve this, set a flag in the WaitQueue while holding m_lock which
determines if threads should be blocked at all.
This commit is contained in:
Tom 2021-01-23 22:30:10 -07:00 • committed by Andreas Kling
parent 4cf0859612
commit bd73102513
3 changed files with 42 additions and 17 deletions
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12
Kernel/WaitQueue.cpp
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@ -35,17 +35,18 @@ bool WaitQueue::should_add_blocker(Thread::Blocker& b, void* data)
ASSERT(data != nullptr); // Thread that is requesting to be blocked
ASSERT(m_lock.is_locked());
ASSERT(b.blocker_type() == Thread::Blocker::Type::Queue);
if (m_wake_requested) {
if (m_wake_requested || !m_should_block) {
m_wake_requested = false;
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: do not block thread {}, wake was pending", this, data);
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: do not block thread {}, {}", this, data, m_should_block ? "wake was pending" : "not blocking");
return false;
}
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: should block thread {}", this, data);
return true;
}
void WaitQueue::wake_one()
u32 WaitQueue::wake_one()
{
u32 did_wake = 0;
ScopedSpinLock lock(m_lock);
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: wake_one", this);
bool did_unblock_one = do_unblock([&](Thread::Blocker& b, void* data, bool& stop_iterating) {
@ -55,11 +56,14 @@ void WaitQueue::wake_one()
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: wake_one unblocking {}", this, data);
if (blocker.unblock()) {
stop_iterating = true;
did_wake = 1;
return true;
}
return false;
});
m_wake_requested = !did_unblock_one;
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: wake_one woke {} threads", this, did_wake);
return did_wake;
}
u32 WaitQueue::wake_n(u32 wake_count)
@ -84,6 +88,7 @@ u32 WaitQueue::wake_n(u32 wake_count)
return false;
});
m_wake_requested = !did_unblock_some;
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: wake_n({}) woke {} threads", this, wake_count, did_wake);
return did_wake;
}
@ -108,6 +113,7 @@ u32 WaitQueue::wake_all()
return false;
});
m_wake_requested = !did_unblock_any;
dbgln<WAITQUEUE_DEBUG>("WaitQueue @ {}: wake_all woke {} threads", this, did_wake);
return did_wake;
}