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[kernel] Fix scheduler deadlocks

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The scheduler queue locks could deadlock if the timer fired before the
scoped lock destructor ran. Also, reduce lock contention by letting only
one CPU steal work at a time.
This commit is contained in:
Justin C. Miller
2021-07-15 23:32:35 -07:00
parent 37e385e783
commit edfc5ab8b4
2 changed files with 16 additions and 13 deletions
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11
src/kernel/scheduler.cpp
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@@ -98,6 +98,8 @@ scheduler::start()
{ {
cpu_data &cpu = current_cpu(); cpu_data &cpu = current_cpu();
run_queue &queue = m_run_queues[cpu.index]; run_queue &queue = m_run_queues[cpu.index];
{
kutil::scoped_lock lock {queue.lock}; kutil::scoped_lock lock {queue.lock};
process *kp = &process::kernel_process(); process *kp = &process::kernel_process();
@@ -109,6 +111,7 @@ scheduler::start()
cpu.tcb = tcb; cpu.tcb = tcb;
queue.current = tcb; queue.current = tcb;
}
cpu.apic->enable_timer(isr::isrTimer, false); cpu.apic->enable_timer(isr::isrTimer, false);
cpu.apic->reset_timer(10); cpu.apic->reset_timer(10);
@@ -219,9 +222,6 @@ balance_lists(tcb_list &to, tcb_list &from)
void void
scheduler::steal_work(cpu_data &cpu) scheduler::steal_work(cpu_data &cpu)
{ {
// First grab a scheduler-wide lock to avoid deadlock
kutil::scoped_lock steal_lock {m_steal_lock};
// Lock this cpu's queue for the whole time while we modify it // Lock this cpu's queue for the whole time while we modify it
run_queue &my_queue = m_run_queues[cpu.index]; run_queue &my_queue = m_run_queues[cpu.index];
kutil::scoped_lock my_queue_lock {my_queue.lock}; kutil::scoped_lock my_queue_lock {my_queue.lock};
@@ -255,9 +255,12 @@ scheduler::schedule()
lapic &apic = *cpu.apic; lapic &apic = *cpu.apic;
uint32_t remaining = apic.stop_timer(); uint32_t remaining = apic.stop_timer();
if (m_clock - queue.last_steal > steal_frequency) { // Only one CPU can be stealing at a time
if (m_steal_turn == cpu.index &&
m_clock - queue.last_steal > steal_frequency) {
steal_work(cpu); steal_work(cpu);
queue.last_steal = m_clock; queue.last_steal = m_clock;
m_steal_turn = (m_steal_turn + 1) % m_run_queues.count();
} }
// We need to explicitly lock/unlock here instead of // We need to explicitly lock/unlock here instead of

2
src/kernel/scheduler.h
View File

@@ -97,7 +97,7 @@ private:
// TODO: lol a real clock // TODO: lol a real clock
uint64_t m_clock = 0; uint64_t m_clock = 0;
kutil::spinlock m_steal_lock; unsigned m_steal_turn = 0;
static scheduler *s_instance; static scheduler *s_instance;
}; };