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sched: fix race on thread switching

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Matheus
2026-09-14 13:21:04 -03:00
parent f386f8e33f
commit d1cc050d76
2 changed files with 32 additions and 26 deletions
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kernel-src/sys/scheduler/scheduler.c
+31 -25
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@@ -17,19 +17,23 @@
#define QUANTUM_US 10000
#define SCHEDULER_STACK_SIZE PAGE_SIZE * 16
static __attribute__((noreturn)) void switch_thread(thread_t *thread) {
// requires the current CPU scheduler lock and, when migrating, the destination
// CPU scheduler lock to be held. The locks are released only after the outgoing
// thread context has been saved and ownership has moved to the incoming thread.
static __attribute__((noreturn)) void switch_thread(thread_t *thread, cpu_t *migration_cpu) {
interrupt_set(false);
cpu_t *cpu = current_cpu();
thread_t* current = current_thread();
sched_thread_running_callback(thread);
current_cpu()->thread = thread;
cpu->thread = thread;
if(current == NULL || thread->mmctx != current->mmctx)
mm_switch_context(thread->mmctx);
current_cpu()->intstatus = ARCH_CONTEXT_INTSTATUS(&thread->context);
thread->cpu = current_cpu();
cpu->intstatus = ARCH_CONTEXT_INTSTATUS(&thread->context);
thread->cpu = cpu;
if (current)
current->flags &= ~THREAD_FLAGS_RUNNING;
@@ -41,9 +45,13 @@ static __attribute__((noreturn)) void switch_thread(thread_t *thread) {
thread->flags |= THREAD_FLAGS_RUNNING;
__assert((thread->flags & THREAD_FLAGS_QUEUED) == 0);
void *schedulerstack = current_cpu()->schedulerstack;
void *schedulerstack = cpu->schedulerstack;
__assert(!((void *)thread->context.rsp < schedulerstack && (void *)thread->context.rsp >= (schedulerstack - SCHEDULER_STACK_SIZE)));
if (migration_cpu)
spinlock_release(&migration_cpu->sched_lock);
spinlock_release(&cpu->sched_lock);
ARCH_CONTEXT_SWITCHTHREAD(thread);
__builtin_unreachable();
}
@@ -52,16 +60,16 @@ static __attribute__((noreturn)) void switch_thread(thread_t *thread) {
__attribute__((noreturn)) void sched_stop_current_thread() {
interrupt_set(false);
spinlock_acquire(&current_cpu()->sched_lock);
if (current_thread())
current_thread()->flags &= ~THREAD_FLAGS_RUNNING;
spinlock_acquire(&current_cpu()->sched_lock);
thread_t *next = sched_select_next_thread();
spinlock_release(&current_cpu()->sched_lock);
__assert(next);
switch_thread(next);
switch_thread(next, NULL);
}
typedef struct {
@@ -160,18 +168,16 @@ static void yield(context_t *context, void *) {
thread_t *next = sched_select_next_thread();
if (thread == next)
if (thread == next) {
__assert(sleeping == false);
thread->flags |= THREAD_FLAGS_RUNNING;
spinlock_release(&current_cpu()->sched_lock);
if (next != thread || sleeping) {
ARCH_CONTEXT_THREADSAVE(thread, context);
switch_thread(next);
spinlock_release(&current_cpu()->sched_lock);
sched_thread_running_callback(thread);
return;
}
sched_thread_running_callback(current_thread());
ARCH_CONTEXT_THREADSAVE(thread, context);
switch_thread(next, NULL);
}
int sched_yield() {
@@ -225,9 +231,7 @@ static void dopreempt() {
sched_insert_in_cpu_queue(current_cpu(), current);
thread_t *next = sched_select_next_thread();
spinlock_release(&current_cpu()->sched_lock);
switch_thread(next);
switch_thread(next, NULL);
}
static void sched_reschedule_dpc(context_t *context, dpcarg_t arg) {
@@ -284,22 +288,24 @@ void sched_target_cpu(cpu_t *cpu) {
static void reschedule_yield(context_t *context, void *_cpu) {
thread_t *thread = current_thread();
cpu_t *cpu = _cpu;
cpu_t *source = current_cpu();
ARCH_CONTEXT_THREADSAVE(thread, context);
spinlock_acquire(&cpu->sched_lock);
cpu_t *first = source->internal_id < cpu->internal_id ? source : cpu;
cpu_t *second = first == source ? cpu : source;
spinlock_acquire(&first->sched_lock);
spinlock_acquire(&second->sched_lock);
thread->flags &= ~THREAD_FLAGS_RUNNING;
sched_insert_in_cpu_queue(cpu, thread);
spinlock_release(&cpu->sched_lock);
spinlock_acquire(&current_cpu()->sched_lock);
thread_t *next = sched_select_next_thread();
if (sched_thread_can_run_in_cpu(thread, cpu->last_queue, cpu->last_interactivity))
arch_smp_send_ipi(cpu, cpu->reschedule_isr, ARCH_SMP_IPI_TARGET, false);
spinlock_release(&current_cpu()->sched_lock);
switch_thread(next);
switch_thread(next, cpu);
}
// TODO verify if something like this is really needed