disable interrupts when holding kernel lock

defs.h

@@ -41,6 +41,7 @@ void lapic_init(int);
 void lapic_timerinit(void);
 void lapic_timerintr(void);
 void lapic_enableintr(void);
+void lapic_disableintr(void);
 
 // spinlock.c
 extern uint32_t kernel_lock;

mp.c

@@ -183,6 +183,12 @@ lapic_enableintr(void)
   lapic_write(LAPIC_TPR, 0);
 }
 
+void
+lapic_disableintr(void) 
+{
+  lapic_write(LAPIC_TPR, 0xFF);
+}
+
 int
 cpu(void)
 {

spinlock.c

@@ -14,6 +14,8 @@ acquire_spinlock(uint32_t* lock)
 
   if (*lock == cpu_id)
     return;
+  
+  lapic_disableintr();
   while ( cmpxchg(LOCK_FREE, cpu_id, lock) != cpu_id ) { ; }
   // cprintf ("acquired: %d\n", cpu_id);
 }
@@ -26,6 +28,7 @@ release_spinlock(uint32_t* lock)
   if (*lock != cpu_id)
     panic("release_spinlock: releasing a lock that i don't own\n");
   *lock = LOCK_FREE;
+  lapic_enableintr();
 }
 
 void