sandbox: vm: add synchronisation using spinlocks

sandbox/vm/cache.c

@@ -140,6 +140,9 @@ static unsigned int pointer_to_slot(vm_slab_t *slab, void *p)
 
 void *vm_cache_alloc(vm_cache_t *cache, vm_flags_t flags)
 {
+	unsigned long irq_flags;
+	spin_lock_irqsave(&cache->c_lock, &irq_flags);
+
 	vm_slab_t *slab = NULL;
 	if (!queue_empty(&cache->c_slabs_partial)) {
 		/* prefer using up partially-full slabs before taking a fresh one */
@@ -156,6 +159,7 @@ void *vm_cache_alloc(vm_cache_t *cache, vm_flags_t flags)
 	}
 
 	if (!slab) {
+		spin_unlock_irqrestore(&cache->c_lock, irq_flags);
 		return NULL;
 	}
 
@@ -167,7 +171,8 @@ void *vm_cache_alloc(vm_cache_t *cache, vm_flags_t flags)
 	} else {
 		queue_push_back(&cache->c_slabs_partial, &slab->s_list);
 	}
-		
+
+	spin_unlock_irqrestore(&cache->c_lock, irq_flags);
 	return p;
 }