ladybird/Kernel/Lock.cpp
Brian Gianforcaro 04156d53ca Kernel: Utilize AK::SourceLocation for LOCK_DEBUG instrumentation.
The previous `LOCKER(..)` instrumentation only covered some of the
cases where a lock is actually acquired. By utilizing the new
`AK::SourceLocation` functionality we can now reliably instrument
all calls to lock automatically.

Other changes:
- Tweak the message in `Thread::finalize()` which dumps leaked lock
  so it's more readable and includes the function information that is
  now available.

- Make the `LOCKER(..)` define a no-op, it will be cleaned up in a
  follow up change.
2021-04-25 09:38:27 +02:00

339 lines
12 KiB
C++

/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/SourceLocation.h>
#include <AK/TemporaryChange.h>
#include <Kernel/Debug.h>
#include <Kernel/KSyms.h>
#include <Kernel/Lock.h>
#include <Kernel/Thread.h>
namespace Kernel {
#if LOCK_DEBUG
void Lock::lock(Mode mode, const SourceLocation& location)
#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!
VERIFY(!Processor::current().in_irq());
VERIFY(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) {
// I don't know *who* is using "m_lock", so just yield.
Scheduler::yield_from_critical();
continue;
}
// FIXME: Do not add new readers if writers are queued.
Mode current_mode = m_mode;
switch (current_mode) {
case Mode::Unlocked: {
dbgln_if(LOCK_TRACE_DEBUG, "Lock::lock @ ({}) {}: acquire {}, currently unlocked", this, m_name, mode_to_string(mode));
m_mode = mode;
VERIFY(!m_holder);
VERIFY(m_shared_holders.is_empty());
if (mode == Mode::Exclusive) {
m_holder = current_thread;
} else {
VERIFY(mode == Mode::Shared);
m_shared_holders.set(current_thread, 1);
}
VERIFY(m_times_locked == 0);
m_times_locked++;
#if LOCK_DEBUG
if (current_thread) {
current_thread->holding_lock(*this, 1, location);
}
#endif
m_queue.should_block(true);
m_lock.store(false, AK::memory_order_release);
return;
}
case Mode::Exclusive: {
VERIFY(m_holder);
if (m_holder != current_thread)
break;
VERIFY(m_shared_holders.is_empty());
if constexpr (LOCK_TRACE_DEBUG) {
if (mode == Mode::Exclusive)
dbgln("Lock::lock @ {} ({}): acquire {}, currently exclusive, holding: {}", this, m_name, mode_to_string(mode), m_times_locked);
else
dbgln("Lock::lock @ {} ({}): acquire exclusive (requested {}), currently exclusive, holding: {}", this, m_name, mode_to_string(mode), m_times_locked);
}
VERIFY(mode == Mode::Exclusive || mode == Mode::Shared);
VERIFY(m_times_locked > 0);
m_times_locked++;
#if LOCK_DEBUG
current_thread->holding_lock(*this, 1, location);
#endif
m_lock.store(false, AK::memory_order_release);
return;
}
case Mode::Shared: {
VERIFY(!m_holder);
if (mode != Mode::Shared)
break;
dbgln_if(LOCK_TRACE_DEBUG, "Lock::lock @ {} ({}): acquire {}, currently shared, locks held {}", this, m_name, mode_to_string(mode), m_times_locked);
VERIFY(m_times_locked > 0);
m_times_locked++;
VERIFY(!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, location);
#endif
m_lock.store(false, AK::memory_order_release);
return;
}
default:
VERIFY_NOT_REACHED();
}
m_lock.store(false, AK::memory_order_release);
dbgln_if(LOCK_TRACE_DEBUG, "Lock::lock @ {} ({}) waiting...", this, m_name);
m_queue.wait_forever(m_name);
dbgln_if(LOCK_TRACE_DEBUG, "Lock::lock @ {} ({}) waited", this, m_name);
}
}
void Lock::unlock()
{
// NOTE: This may be called from an interrupt handler (not an IRQ handler)
// and also from within critical sections!
VERIFY(!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, m_name, mode_to_string(current_mode), m_times_locked);
else
dbgln("Lock::unlock @ {} ({}): release {}, holding: {}", this, m_name, mode_to_string(current_mode), m_times_locked);
}
VERIFY(current_mode != Mode::Unlocked);
VERIFY(m_times_locked > 0);
m_times_locked--;
switch (current_mode) {
case Mode::Exclusive:
VERIFY(m_holder == current_thread);
VERIFY(m_shared_holders.is_empty());
if (m_times_locked == 0)
m_holder = nullptr;
break;
case Mode::Shared: {
VERIFY(!m_holder);
auto it = m_shared_holders.find(current_thread);
VERIFY(it != m_shared_holders.end());
if (it->value > 1) {
it->value--;
} else {
VERIFY(it->value > 0);
m_shared_holders.remove(it);
}
break;
}
default:
VERIFY_NOT_REACHED();
}
bool unlocked_last = (m_times_locked == 0);
if (unlocked_last) {
VERIFY(current_mode == Mode::Exclusive ? !m_holder : m_shared_holders.is_empty());
m_mode = Mode::Unlocked;
m_queue.should_block(false);
}
#if LOCK_DEBUG
if (current_thread) {
current_thread->holding_lock(*this, -1, {});
}
#endif
m_lock.store(false, AK::memory_order_release);
if (unlocked_last) {
u32 did_wake = m_queue.wake_one();
dbgln_if(LOCK_TRACE_DEBUG, "Lock::unlock @ {} ({}) wake one ({})", this, m_name, did_wake);
}
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!
VERIFY(!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_if(LOCK_RESTORE_DEBUG, "Lock::force_unlock_if_locked @ {}: unlocking exclusive with lock count: {}", this, m_times_locked);
#if LOCK_DEBUG
m_holder->holding_lock(*this, -(int)m_times_locked, {});
#endif
m_holder = nullptr;
VERIFY(m_times_locked > 0);
lock_count_to_restore = m_times_locked;
m_times_locked = 0;
m_mode = Mode::Unlocked;
m_queue.should_block(false);
m_lock.store(false, AK::memory_order_release);
previous_mode = Mode::Exclusive;
break;
}
case Mode::Shared: {
VERIFY(!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_if(LOCK_RESTORE_DEBUG, "Lock::force_unlock_if_locked @ {}: unlocking exclusive with lock count: {}, total locks: {}",
this, it->value, m_times_locked);
VERIFY(it->value > 0);
lock_count_to_restore = it->value;
VERIFY(lock_count_to_restore > 0);
#if LOCK_DEBUG
m_holder->holding_lock(*this, -(int)lock_count_to_restore, {});
#endif
m_shared_holders.remove(it);
VERIFY(m_times_locked >= lock_count_to_restore);
m_times_locked -= lock_count_to_restore;
if (m_times_locked == 0) {
m_mode = Mode::Unlocked;
m_queue.should_block(false);
}
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:
VERIFY_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, const SourceLocation& location)
#else
void Lock::restore_lock(Mode mode, u32 lock_count)
#endif
{
VERIFY(mode != Mode::Unlocked);
VERIFY(lock_count > 0);
VERIFY(!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_if(LOCK_RESTORE_DEBUG, "Lock::restore_lock @ {}: restoring {} with lock count {}, was unlocked", this, mode_to_string(mode), lock_count);
VERIFY(m_times_locked == 0);
m_times_locked = lock_count;
VERIFY(!m_holder);
VERIFY(m_shared_holders.is_empty());
m_holder = current_thread;
m_queue.should_block(true);
m_lock.store(false, AK::memory_order_release);
#if LOCK_DEBUG
m_holder->holding_lock(*this, (int)lock_count, location);
#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_if(LOCK_RESTORE_DEBUG, "Lock::restore_lock @ {}: restoring {} with lock count {}, was {}",
this, mode_to_string(mode), lock_count, mode_to_string(expected_mode));
VERIFY(expected_mode == Mode::Shared || m_times_locked == 0);
m_times_locked += lock_count;
VERIFY(!m_holder);
VERIFY((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
VERIFY(set_result == AK::HashSetResult::InsertedNewEntry);
m_queue.should_block(true);
m_lock.store(false, AK::memory_order_release);
#if LOCK_DEBUG
m_holder->holding_lock(*this, (int)lock_count, location);
#endif
return;
}
default:
VERIFY_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()
{
VERIFY(m_mode != Mode::Shared);
m_queue.wake_all();
}
}