Replace interrupt masking with spinlock in mqueue for SMP support

The original message queue implementation used CRITICAL_ENTER() and
CRITICAL_LEAVE() to protect critical sections by disabling interrupts.
This was sufficient for single-core systems, where only one hart could
execute tasks.

To support SMP, we replace these macros with a proper spinlock using
RV32A atomic instructions. This ensures safe access to the internal
queue structures when multiple harts concurrently interact with message
queues.

This change eliminates potential race conditions in message queue
operations as we move toward multi-hart scheduling.

Author: visitorckw

kernel/mqueue.c

@@ -6,8 +6,13 @@
 #include <sys/mqueue.h>
 #include <sys/task.h>
 
+#include <spinlock.h>
+
 #include "private/error.h"
 
+static spinlock_t queue_lock = SPINLOCK_INITIALIZER;
+static uint32_t queue_flags = 0;
+
 mq_t *mo_mq_create(uint16_t max_items)
 {
     mq_t *mq = malloc(sizeof *mq);
@@ -24,27 +29,27 @@ mq_t *mo_mq_create(uint16_t max_items)
 
 int32_t mo_mq_destroy(mq_t *mq)
 {
-    CRITICAL_ENTER();
+    spin_lock_irqsave(&queue_lock, &queue_flags);
 
     if (queue_count(mq->q) != 0) { /* refuse to destroy non-empty q */
-        CRITICAL_LEAVE();
+        spin_unlock_irqrestore(&queue_lock, queue_flags);
         return ERR_MQ_NOTEMPTY;
     }
 
     queue_destroy(mq->q);
     free(mq);
 
-    CRITICAL_LEAVE();
+    spin_unlock_irqrestore(&queue_lock, queue_flags);
     return ERR_OK;
 }
 
 int32_t mo_mq_enqueue(mq_t *mq, message_t *msg)
 {
     int32_t rc;
 
-    CRITICAL_ENTER();
+    spin_lock_irqsave(&queue_lock, &queue_flags);
     rc = queue_enqueue(mq->q, msg);
-    CRITICAL_LEAVE();
+    spin_unlock_irqrestore(&queue_lock, queue_flags);
 
     return rc; /* 0 on success, −1 on full */
 }
@@ -54,9 +59,9 @@ message_t *mo_mq_dequeue(mq_t *mq)
 {
     message_t *msg;
 
-    CRITICAL_ENTER();
+    spin_lock_irqsave(&queue_lock, &queue_flags);
     msg = queue_dequeue(mq->q);
-    CRITICAL_LEAVE();
+    spin_unlock_irqrestore(&queue_lock, queue_flags);
 
     return msg; /* NULL when queue is empty */
 }
@@ -66,9 +71,9 @@ message_t *mo_mq_peek(mq_t *mq)
 {
     message_t *msg;
 
-    CRITICAL_ENTER();
+    spin_lock_irqsave(&queue_lock, &queue_flags);
     msg = queue_peek(mq->q);
-    CRITICAL_LEAVE();
+    spin_unlock_irqrestore(&queue_lock, queue_flags);
 
     return msg; /* NULL when queue is empty */
 }