/* * Copyright (c) 2018-2020, Andreas Kling * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * 1. Redistributions of source code must retain the above copyright notice, this * list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright notice, * this list of conditions and the following disclaimer in the documentation * and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ #include #include #include #include #include namespace Kernel { #if LOCK_DEBUG void Lock::lock(Mode mode) { lock("unknown", 0, mode); } void Lock::lock(const char* file, int line, Mode mode) #else void Lock::lock(Mode mode) #endif { // NOTE: This may be called from an interrupt handler (not an IRQ handler) // and also from within critical sections! ASSERT(!Processor::current().in_irq()); ASSERT(mode != Mode::Unlocked); auto current_thread = Thread::current(); ScopedCritical critical; // in case we're not in a critical section already for (;;) { if (m_lock.exchange(true, AK::memory_order_acq_rel) == false) { do { // FIXME: Do not add new readers if writers are queued. Mode current_mode = m_mode; switch (current_mode) { case Mode::Unlocked: { dbgln("Lock::lock @ {}: acquire {}, currently unlocked", this, mode_to_string(mode)); m_mode = mode; ASSERT(!m_holder); ASSERT(m_shared_holders.is_empty()); if (mode == Mode::Exclusive) { m_holder = current_thread; } else { ASSERT(mode == Mode::Shared); m_shared_holders.set(current_thread, 1); } ASSERT(m_times_locked == 0); m_times_locked++; #if LOCK_DEBUG current_thread->holding_lock(*this, 1, file, line); #endif m_lock.store(false, AK::memory_order_release); return; } case Mode::Exclusive: { ASSERT(m_holder); if (m_holder != current_thread) break; ASSERT(m_shared_holders.is_empty()); if constexpr (LOCK_TRACE_DEBUG) { if (mode == Mode::Exclusive) dbgln("Lock::lock @ {}: acquire {}, currently exclusive, holding: {}", this, mode_to_string(mode), m_times_locked); else dbgln("Lock::lock @ {}: acquire exclusive (requested {}), currently exclusive, holding: {}", this, mode_to_string(mode), m_times_locked); } ASSERT(mode == Mode::Exclusive || mode == Mode::Shared); ASSERT(m_times_locked > 0); m_times_locked++; #if LOCK_DEBUG current_thread->holding_lock(*this, 1, file, line); #endif m_lock.store(false, AK::memory_order_release); return; } case Mode::Shared: { ASSERT(!m_holder); if (mode != Mode::Shared) break; dbgln("Lock::lock @ {}: acquire {}, currently shared, locks held {}", this, mode_to_string(mode), m_times_locked); ASSERT(m_times_locked > 0); m_times_locked++; ASSERT(!m_shared_holders.is_empty()); auto it = m_shared_holders.find(current_thread); if (it != m_shared_holders.end()) it->value++; else m_shared_holders.set(current_thread, 1); #if LOCK_DEBUG current_thread->holding_lock(*this, 1, file, line); #endif m_lock.store(false, AK::memory_order_release); return; } default: ASSERT_NOT_REACHED(); } m_lock.store(false, AK::memory_order_release); } while (m_queue.wait_on({}, m_name) == Thread::BlockResult::NotBlocked); } else { // I don't know *who* is using "m_lock", so just yield. Scheduler::yield_from_critical(); } } } void Lock::unlock() { // NOTE: This may be called from an interrupt handler (not an IRQ handler) // and also from within critical sections! ASSERT(!Processor::current().in_irq()); auto current_thread = Thread::current(); ScopedCritical critical; // in case we're not in a critical section already for (;;) { if (m_lock.exchange(true, AK::memory_order_acq_rel) == false) { Mode current_mode = m_mode; if constexpr (LOCK_TRACE_DEBUG) { if (current_mode == Mode::Shared) dbgln("Lock::unlock @ {}: release {}, locks held: {}", this, mode_to_string(current_mode), m_times_locked); else dbgln("Lock::unlock @ {}: release {}, holding: {}", this, mode_to_string(current_mode), m_times_locked); } ASSERT(current_mode != Mode::Unlocked); ASSERT(m_times_locked > 0); m_times_locked--; switch (current_mode) { case Mode::Exclusive: ASSERT(m_holder == current_thread); ASSERT(m_shared_holders.is_empty()); if (m_times_locked == 0) m_holder = nullptr; break; case Mode::Shared: { ASSERT(!m_holder); auto it = m_shared_holders.find(current_thread); ASSERT(it != m_shared_holders.end()); if (it->value > 1) { it->value--; } else { ASSERT(it->value > 0); m_shared_holders.remove(it); } break; } default: ASSERT_NOT_REACHED(); } if (m_times_locked == 0) { ASSERT(current_mode == Mode::Exclusive ? !m_holder : m_shared_holders.is_empty()); m_mode = Mode::Unlocked; } #if LOCK_DEBUG current_thread->holding_lock(*this, -1); #endif m_lock.store(false, AK::memory_order_release); m_queue.wake_one(); return; } // I don't know *who* is using "m_lock", so just yield. Scheduler::yield_from_critical(); } } auto Lock::force_unlock_if_locked(u32& lock_count_to_restore) -> Mode { // NOTE: This may be called from an interrupt handler (not an IRQ handler) // and also from within critical sections! ASSERT(!Processor::current().in_irq()); auto current_thread = Thread::current(); ScopedCritical critical; // in case we're not in a critical section already for (;;) { if (m_lock.exchange(true, AK::memory_order_acq_rel) == false) { Mode previous_mode; auto current_mode = m_mode.load(AK::MemoryOrder::memory_order_relaxed); switch (current_mode) { case Mode::Exclusive: { if (m_holder != current_thread) { m_lock.store(false, AK::MemoryOrder::memory_order_release); lock_count_to_restore = 0; return Mode::Unlocked; } dbgln("Lock::force_unlock_if_locked @ {}: unlocking exclusive with lock count: {}", this, m_times_locked); m_holder = nullptr; ASSERT(m_times_locked > 0); lock_count_to_restore = m_times_locked; m_times_locked = 0; m_mode = Mode::Unlocked; m_lock.store(false, AK::memory_order_release); #if LOCK_DEBUG m_holder->holding_lock(*this, -(int)lock_count_to_restore); #endif previous_mode = Mode::Exclusive; break; } case Mode::Shared: { ASSERT(!m_holder); auto it = m_shared_holders.find(current_thread); if (it == m_shared_holders.end()) { m_lock.store(false, AK::MemoryOrder::memory_order_release); lock_count_to_restore = 0; return Mode::Unlocked; } dbgln("Lock::force_unlock_if_locked @ {}: unlocking exclusive with lock count: {}, total locks: {}", this, it->value, m_times_locked); ASSERT(it->value > 0); lock_count_to_restore = it->value; ASSERT(lock_count_to_restore > 0); #if LOCK_DEBUG m_holder->holding_lock(*this, -(int)lock_count_to_restore); #endif m_shared_holders.remove(it); ASSERT(m_times_locked >= lock_count_to_restore); m_times_locked -= lock_count_to_restore; if (m_times_locked == 0) m_mode = Mode::Unlocked; m_lock.store(false, AK::memory_order_release); previous_mode = Mode::Shared; break; } case Mode::Unlocked: { m_lock.store(false, AK::memory_order_relaxed); lock_count_to_restore = 0; previous_mode = Mode::Unlocked; break; } default: ASSERT_NOT_REACHED(); } m_queue.wake_one(); return previous_mode; } // I don't know *who* is using "m_lock", so just yield. Scheduler::yield_from_critical(); } } #if LOCK_DEBUG void Lock::restore_lock(Mode mode, u32 lock_count) { return restore_lock("unknown", 0, mode, lock_count); } void Lock::restore_lock(const char* file, int line, Mode mode, u32 lock_count) #else void Lock::restore_lock(Mode mode, u32 lock_count) #endif { ASSERT(mode != Mode::Unlocked); ASSERT(lock_count > 0); ASSERT(!Processor::current().in_irq()); auto current_thread = Thread::current(); ScopedCritical critical; // in case we're not in a critical section already for (;;) { if (m_lock.exchange(true, AK::memory_order_acq_rel) == false) { switch (mode) { case Mode::Exclusive: { auto expected_mode = Mode::Unlocked; if (!m_mode.compare_exchange_strong(expected_mode, Mode::Exclusive)) break; dbgln("Lock::restore_lock @ {}: restoring {} with lock count {}, was unlocked", this, mode_to_string(mode), lock_count); ASSERT(m_times_locked == 0); m_times_locked = lock_count; ASSERT(!m_holder); ASSERT(m_shared_holders.is_empty()); m_holder = current_thread; m_lock.store(false, AK::memory_order_release); #if LOCK_DEBUG m_holder->holding_lock(*this, (int)lock_count, file, line); #endif return; } case Mode::Shared: { auto expected_mode = Mode::Unlocked; if (!m_mode.compare_exchange_strong(expected_mode, Mode::Shared) && expected_mode != Mode::Shared) break; dbgln("Lock::restore_lock @ {}: restoring {} with lock count {}, was {}", this, mode_to_string(mode), lock_count, mode_to_string(expected_mode)); ASSERT(expected_mode == Mode::Shared || m_times_locked == 0); m_times_locked += lock_count; ASSERT(!m_holder); ASSERT((expected_mode == Mode::Unlocked) == m_shared_holders.is_empty()); auto set_result = m_shared_holders.set(current_thread, lock_count); // There may be other shared lock holders already, but we should not have an entry yet ASSERT(set_result == AK::HashSetResult::InsertedNewEntry); m_lock.store(false, AK::memory_order_release); #if LOCK_DEBUG m_holder->holding_lock(*this, (int)lock_count, file, line); #endif return; } default: ASSERT_NOT_REACHED(); } m_lock.store(false, AK::memory_order_relaxed); } // I don't know *who* is using "m_lock", so just yield. Scheduler::yield_from_critical(); } } void Lock::clear_waiters() { ASSERT(m_mode != Mode::Shared); m_queue.wake_all(); } }