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7593418b77
There is a race condition where we would remove a FutexQueue from our futex map and in the meanwhile another thread started to queue itself into that very same futex, leading to that thread to wait forever as no other wake operation could discover that removed FutexQueue. This fixes the problem by: * Tracking imminent waits, which prevents a new FutexQueue from being deleted that a thread will wait on momentarily * Atomically marking a FutexQueue as removed, which prevents a thread from waiting on it before it is actually removed from the futex map.
60 lines
1.7 KiB
C++
60 lines
1.7 KiB
C++
/*
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* Copyright (c) 2020, the SerenityOS developers.
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Atomic.h>
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#include <AK/RefCounted.h>
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#include <Kernel/SpinLock.h>
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#include <Kernel/Thread.h>
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#include <Kernel/VM/VMObject.h>
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namespace Kernel {
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class FutexQueue : public Thread::BlockCondition
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, public RefCounted<FutexQueue>
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, public VMObjectDeletedHandler {
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public:
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FutexQueue(FlatPtr user_address_or_offset, VMObject* vmobject = nullptr);
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virtual ~FutexQueue();
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u32 wake_n_requeue(u32, const Function<FutexQueue*()>&, u32, bool&, bool&);
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u32 wake_n(u32, const Optional<u32>&, bool&);
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u32 wake_all(bool&);
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template<class... Args>
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Thread::BlockResult wait_on(const Thread::BlockTimeout& timeout, Args&&... args)
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{
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return Thread::current()->block<Thread::FutexBlocker>(timeout, *this, forward<Args>(args)...);
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}
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virtual void vmobject_deleted(VMObject&) override;
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bool queue_imminent_wait();
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void did_remove();
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bool try_remove();
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bool is_empty_and_no_imminent_waits()
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{
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ScopedSpinLock lock(m_lock);
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return is_empty_and_no_imminent_waits_locked();
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}
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bool is_empty_and_no_imminent_waits_locked();
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protected:
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virtual bool should_add_blocker(Thread::Blocker& b, void* data) override;
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private:
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// For private futexes we just use the user space address.
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// But for global futexes we use the offset into the VMObject
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const FlatPtr m_user_address_or_offset;
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WeakPtr<VMObject> m_vmobject;
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const bool m_is_global;
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size_t m_imminent_waits { 1 }; // We only create this object if we're going to be waiting, so start out with 1
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bool m_was_removed { false };
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};
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}
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