resource allocator: make interrupt safe

kernel-src/include/resource_allocator.h

@@ -4,7 +4,7 @@
 // simple FIFO allocator for an arbritary resource
 
 #include <kernel/scheduler.h>
-#include <mutex.h>
+#include <spinlock.h>
 
 // TODO move this to a proper dequeue abstraction
 typedef struct resource_allocator_waiter_t {
@@ -14,7 +14,7 @@ typedef struct resource_allocator_waiter_t {
 } resource_allocator_waiter_t;
 
 typedef struct {
-	mutex_t mutex;
+	spinlock_t spinlock; // a spinlock is used to allow freeing in an interrupt context
 	resource_allocator_waiter_t *queue;
 	resource_allocator_waiter_t *tail;
 	size_t resource_current;
@@ -22,7 +22,7 @@ typedef struct {
 } resource_allocator_t;
 
 void resource_allocator_init(resource_allocator_t *allocator, size_t resource_total, size_t allocate_max);
-void resource_allocate(resource_allocator_t *allocator, size_t count);
+size_t resource_allocate(resource_allocator_t *allocator, size_t count);
 void resource_free(resource_allocator_t *allocator, size_t count);
 
 #endif

kernel-src/lib/resource_allocator.c

@@ -18,14 +18,15 @@ static void pop(resource_allocator_t *allocator) {
 }
 
 void resource_allocator_init(resource_allocator_t *allocator, size_t resource_total, size_t allocate_max) {
-	MUTEX_INIT(&allocator->mutex);
+	SPINLOCK_INIT(allocator->spinlock);
 	allocator->queue = allocator->tail = NULL;
 	allocator->resource_current = resource_total;
 	allocator->allocate_max = allocate_max;
 }
 
-void resource_allocate(resource_allocator_t *allocator, size_t count) {
+size_t resource_allocate(resource_allocator_t *allocator, size_t count) {
-	MUTEX_ACQUIRE(&allocator->mutex);
+	count = min(allocator->allocate_max, count);
+	bool status = spinlock_acquire_irq_clear(&allocator->spinlock);
 
 	if (allocator->queue || allocator->resource_current < count) {
 		resource_allocator_waiter_t waiter = {
@@ -36,19 +37,19 @@ void resource_allocate(resource_allocator_t *allocator, size_t count) {
 
 		insert(allocator, &waiter);
 		sched_prepare_sleep(false);
-		MUTEX_RELEASE(&allocator->mutex);
+		spinlock_release(&allocator->spinlock);
 		sched_yield();
-		return;
+		return count;
 	}
 
 	allocator->resource_current -= count;
 	
-	MUTEX_RELEASE(&allocator->mutex);
+	spinlock_release_irq_restore(&allocator->spinlock, status);
+	return count;
 }
 
 void resource_free(resource_allocator_t *allocator, size_t count) {
-	count = min(allocator->allocate_max, count);
+	bool status = spinlock_acquire_irq_clear(&allocator->spinlock);
-	MUTEX_ACQUIRE(&allocator->mutex);
 
 	allocator->resource_current += count;
 
@@ -58,5 +59,5 @@ void resource_free(resource_allocator_t *allocator, size_t count) {
 		pop(allocator);
 	}
 	
-	MUTEX_RELEASE(&allocator->mutex);
+	spinlock_release_irq_restore(&allocator->spinlock, status);
 }