mirror of
https://github.com/RGBCube/serenity
synced 2025-05-25 22:25:08 +00:00
Kernel: Fix Lock race causing infinite spinning between two threads
We need to account for how many shared lock instances the current thread owns, so that we can properly release such references when yielding execution. We also need to release the process lock when donating.
This commit is contained in:
Tom
Andreas Kling
parent
56701f91f9
commit
c4176b0da1
10 changed files with 359 additions and 96 deletions
285
Kernel/Lock.cpp
285
Kernel/Lock.cpp
|
|
@ -27,6 +27,10 @@
|
|||
#include <AK/TemporaryChange.h>
|
||||
#include <Kernel/KSyms.h>
|
||||
#include <Kernel/Lock.h>
|
||||
#include <Kernel/Thread.h>
|
||||
|
||||
//#define LOCK_TRACE_DEBUG
|
||||
//#define LOCK_RESTORE_DEBUG
|
||||
|
||||
namespace Kernel {
|
||||
|
||||
|
|
@ -46,38 +50,78 @@ void Lock::lock(Mode mode)
|
|||
ASSERT(!Processor::current().in_irq());
|
||||
ASSERT(mode != Mode::Unlocked);
|
||||
auto current_thread = Thread::current();
|
||||
ScopedCritical critical;
|
||||
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.
|
||||
bool can_lock;
|
||||
switch (m_mode) {
|
||||
case Lock::Mode::Unlocked:
|
||||
can_lock = true;
|
||||
break;
|
||||
case Lock::Mode::Shared:
|
||||
can_lock = (mode == Lock::Mode::Shared);
|
||||
break;
|
||||
case Lock::Mode::Exclusive:
|
||||
can_lock = (m_holder == current_thread);
|
||||
break;
|
||||
}
|
||||
if (can_lock) {
|
||||
// We got the lock!
|
||||
if (m_mode == Lock::Mode::Unlocked) {
|
||||
m_mode = mode;
|
||||
ASSERT(m_times_locked == 0);
|
||||
if (mode == Mode::Exclusive)
|
||||
m_holder = current_thread;
|
||||
}
|
||||
#ifdef LOCK_DEBUG
|
||||
current_thread->holding_lock(*this, true, file, line);
|
||||
auto current_mode = m_mode.load(AK::MemoryOrder::memory_order_relaxed);
|
||||
switch (current_mode) {
|
||||
case Mode::Unlocked: {
|
||||
#ifdef LOCK_TRACE_DEBUG
|
||||
dbg() << "Lock::lock @ " << this << ": acquire " << mode_to_string(mode) << ", currently unlocked";
|
||||
#endif
|
||||
m_mode.store(mode, AK::MemoryOrder::memory_order_relaxed);
|
||||
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++;
|
||||
#ifdef 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());
|
||||
#ifdef LOCK_TRACE_DEBUG
|
||||
if (mode == Mode::Exclusive)
|
||||
dbg() << "Lock::lock @ " << this << ": acquire " << mode_to_string(mode) << ", currently exclusive, holding: " << m_times_locked;
|
||||
else
|
||||
dbg() << "Lock::lock @ " << this << ": acquire exclusive (requested " << mode_to_string(mode) << "), currently exclusive, holding " << m_times_locked;
|
||||
#endif
|
||||
ASSERT(mode == Mode::Exclusive || mode == Mode::Shared);
|
||||
ASSERT(m_times_locked > 0);
|
||||
m_times_locked++;
|
||||
#ifdef 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;
|
||||
#ifdef LOCK_TRACE_DEBUG
|
||||
dbg() << "Lock::lock @ " << this << ": acquire " << mode_to_string(mode) << ", currently shared, locks held: " << m_times_locked;
|
||||
#endif
|
||||
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);
|
||||
#ifdef 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(nullptr, m_name) == Thread::BlockResult::NotBlocked);
|
||||
} else {
|
||||
|
|
@ -93,28 +137,53 @@ void Lock::unlock()
|
|||
// and also from within critical sections!
|
||||
ASSERT(!Processor::current().in_irq());
|
||||
auto current_thread = Thread::current();
|
||||
ScopedCritical critical;
|
||||
ScopedCritical critical; // in case we're not in a critical section already
|
||||
for (;;) {
|
||||
if (m_lock.exchange(true, AK::memory_order_acq_rel) == false) {
|
||||
ASSERT(m_times_locked);
|
||||
--m_times_locked;
|
||||
auto current_mode = m_mode.load(AK::MemoryOrder::memory_order_relaxed);
|
||||
#ifdef LOCK_TRACE_DEBUG
|
||||
if (current_mode == Mode::Shared)
|
||||
dbg() << "Lock::unlock @ " << this << ": release " << mode_to_string(current_mode) << ", locks held: " << m_times_locked;
|
||||
else
|
||||
dbg() << "Lock::unlock @ " << this << ": release " << mode_to_string(current_mode) << ", holding: " << m_times_locked;
|
||||
#endif
|
||||
ASSERT(current_mode != Mode::Unlocked);
|
||||
|
||||
ASSERT(m_mode != Mode::Unlocked);
|
||||
ASSERT(m_times_locked > 0);
|
||||
m_times_locked--;
|
||||
|
||||
if (m_mode == Mode::Exclusive) {
|
||||
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.store(Mode::Unlocked, AK::MemoryOrder::memory_order_relaxed);
|
||||
}
|
||||
|
||||
#ifdef LOCK_DEBUG
|
||||
current_thread->holding_lock(*this, false);
|
||||
current_thread->holding_lock(*this, -1);
|
||||
#endif
|
||||
|
||||
if (m_times_locked > 0) {
|
||||
m_lock.store(false, AK::memory_order_release);
|
||||
return;
|
||||
}
|
||||
m_mode = Mode::Unlocked;
|
||||
m_lock.store(false, AK::memory_order_release);
|
||||
m_queue.wake_one();
|
||||
return;
|
||||
|
|
@ -124,39 +193,153 @@ void Lock::unlock()
|
|||
}
|
||||
}
|
||||
|
||||
bool Lock::force_unlock_if_locked()
|
||||
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());
|
||||
ScopedCritical critical;
|
||||
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) {
|
||||
if (m_holder != Thread::current()) {
|
||||
m_lock.store(false, AK::MemoryOrder::memory_order_release);
|
||||
return false;
|
||||
}
|
||||
ASSERT(m_mode != Mode::Shared);
|
||||
ASSERT(m_times_locked == 1);
|
||||
#ifdef LOCK_DEBUG
|
||||
m_holder->holding_lock(*this, 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;
|
||||
}
|
||||
#ifdef LOCK_RESTORE_DEBUG
|
||||
dbg() << "Lock::force_unlock_if_locked @ " << this << ": unlocking exclusive with lock count: " << m_times_locked;
|
||||
#endif
|
||||
m_holder = nullptr;
|
||||
m_mode = Mode::Unlocked;
|
||||
m_times_locked = 0;
|
||||
m_lock.store(false, AK::memory_order_release);
|
||||
m_holder = nullptr;
|
||||
ASSERT(m_times_locked > 0);
|
||||
lock_count_to_restore = m_times_locked;
|
||||
m_times_locked = 0;
|
||||
m_mode.store(Mode::Unlocked, AK::MemoryOrder::memory_order_relaxed);
|
||||
m_lock.store(false, AK::memory_order_release);
|
||||
#ifdef 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;
|
||||
}
|
||||
#ifdef LOCK_RESTORE_DEBUG
|
||||
dbg() << "Lock::force_unlock_if_locked @ " << this << ": unlocking exclusive with lock count: " << it->value << ", total locks: " << m_times_locked;
|
||||
#endif
|
||||
ASSERT(it->value > 0);
|
||||
lock_count_to_restore = it->value;
|
||||
ASSERT(lock_count_to_restore > 0);
|
||||
#ifdef 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.store(Mode::Unlocked, AK::MemoryOrder::memory_order_relaxed);
|
||||
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();
|
||||
break;
|
||||
return previous_mode;
|
||||
}
|
||||
// I don't know *who* is using "m_lock", so just yield.
|
||||
Scheduler::yield_from_critical();
|
||||
}
|
||||
}
|
||||
|
||||
#ifdef 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, AK::MemoryOrder::memory_order_relaxed))
|
||||
break;
|
||||
#ifdef LOCK_RESTORE_DEBUG
|
||||
dbg() << "Lock::restore_lock @ " << this << ": restoring " << mode_to_string(mode) << " with lock count " << lock_count << ", was unlocked";
|
||||
#endif
|
||||
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);
|
||||
#ifdef 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, AK::MemoryOrder::memory_order_relaxed) && expected_mode != Mode::Shared)
|
||||
break;
|
||||
#ifdef LOCK_RESTORE_DEBUG
|
||||
dbg() << "Lock::restore_lock @ " << this << ": restoring " << mode_to_string(mode) << " with lock count " << lock_count << ", was " << mode_to_string(expected_mode);
|
||||
#endif
|
||||
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);
|
||||
#ifdef 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();
|
||||
}
|
||||
return true;
|
||||
}
|
||||
|
||||
void Lock::clear_waiters()
|
||||
{
|
||||
ASSERT(m_mode != Mode::Shared);
|
||||
ASSERT(m_mode.load(AK::MemoryOrder::memory_order_relaxed) != Mode::Shared);
|
||||
m_queue.wake_all();
|
||||
}
|
||||
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue