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Kernel: Enhance WaitQueue to remember pending wakes

Browse source 
If WaitQueue::wake_all, WaitQueue::wake_one, or WaitQueue::wake_n
is called but nobody is currently waiting, we should remember that
fact and prevent someone from waiting after such a request. This
solves a race condition where the Finalizer thread is notified
to finalize a thread, but it is not (yet) waiting on this queue.

Fixes #2693
This commit is contained in:
Tom 2020-07-05 15:46:51 -06:00 • committed by Andreas Kling
parent 2a82a25fec
commit 9725bda63e
5 changed files with 93 additions and 27 deletions
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78
Kernel/WaitQueue.cpp
View file

@ -27,8 +27,11 @@
#include <Kernel/Thread.h>
#include <Kernel/WaitQueue.h>
//#define WAITQUEUE_DEBUG
namespace Kernel {
WaitQueue::WaitQueue()
{
}
@ -37,10 +40,20 @@ WaitQueue::~WaitQueue()
{
}
void WaitQueue::enqueue(Thread& thread)
bool WaitQueue::enqueue(Thread& thread)
{
ScopedSpinLock queue_lock(m_lock);
if (m_wake_requested) {
// wake_* was called when no threads were in the queue
// we shouldn't wait at all
m_wake_requested = false;
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": enqueue: wake_all pending";
#endif
return false;
}
m_threads.append(thread);
return true;
}
void WaitQueue::wake_one(Atomic<bool>* lock)
@ -48,42 +61,87 @@ void WaitQueue::wake_one(Atomic<bool>* lock)
ScopedSpinLock queue_lock(m_lock);
if (lock)
*lock = false;
if (m_threads.is_empty())
if (m_threads.is_empty()) {
// Save the fact that a wake was requested
m_wake_requested = true;
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_one: nobody to wake, mark as pending";
#endif
return;
if (auto* thread = m_threads.take_first())
thread->wake_from_queue();
}
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_one:";
#endif
auto* thread = m_threads.take_first();
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_one: wake thread " << *thread;
#endif
thread->wake_from_queue();
m_wake_requested = false;
Scheduler::yield();
}
void WaitQueue::wake_n(i32 wake_count)
void WaitQueue::wake_n(u32 wake_count)
{
ScopedSpinLock queue_lock(m_lock);
if (m_threads.is_empty())
if (m_threads.is_empty()) {
// Save the fact that a wake was requested
m_wake_requested = true;
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_n: nobody to wake, mark as pending";
#endif
return;
}
for (i32 i = 0; i < wake_count; ++i) {
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_n: " << wake_count;
#endif
for (u32 i = 0; i < wake_count; ++i) {
Thread* thread = m_threads.take_first();
if (!thread)
break;
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_n: wake thread " << *thread;
#endif
thread->wake_from_queue();
}
m_wake_requested = false;
Scheduler::yield();
}
void WaitQueue::wake_all()
{
ScopedSpinLock queue_lock(m_lock);
if (m_threads.is_empty())
if (m_threads.is_empty()) {
// Save the fact that a wake was requested
m_wake_requested = true;
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_all: nobody to wake, mark as pending";
#endif
return;
while (!m_threads.is_empty())
m_threads.take_first()->wake_from_queue();
}
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_all: ";
#endif
while (!m_threads.is_empty()) {
Thread* thread = m_threads.take_first();
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": wake_all: wake thread " << *thread;
#endif
thread->wake_from_queue();
}
m_wake_requested = false;
Scheduler::yield();
}
void WaitQueue::clear()
{
ScopedSpinLock queue_lock(m_lock);
#ifdef WAITQUEUE_DEBUG
dbg() << "WaitQueue " << VirtualAddress(this) << ": clear";
#endif
m_threads.clear();
m_wake_requested = false;
}
}