Make sure schedule() is called safely

diff -r dc9246357cdb extras/mini-os/hypervisor.c
@@ -33,6 +33,8 @@
     ((sh)->evtchn_pending[idx] &                \
      ~(sh)->evtchn_mask[idx])
 
+int in_callback;
+
 void do_hypervisor_callback(struct pt_regs *regs)
 {
     unsigned long  l1, l2, l1i, l2i;

@@ -41,6 +43,7 @@ void do_hypervisor_callback(struct pt_re
     shared_info_t *s = HYPERVISOR_shared_info;
     vcpu_info_t   *vcpu_info = &s->vcpu_info[cpu];
 
+    in_callback = 1;
    
     vcpu_info->evtchn_upcall_pending = 0;
     /* NB. No need for a barrier here -- XCHG is a barrier on x86. */

@@ -59,6 +62,8 @@ void do_hypervisor_callback(struct pt_re
 			do_event(port, regs);
         }
     }
+
+    in_callback = 0;
 }
 
 

diff -r dc9246357cdb extras/mini-os/include/hypervisor.h
@@ -42,4 +42,6 @@ void unmask_evtchn(u32 port);
 void unmask_evtchn(u32 port);
 void clear_evtchn(u32 port);
 
+extern int in_callback;
+
 #endif /* __HYPERVISOR_H__ */

diff -r dc9246357cdb extras/mini-os/sched.c
@@ -125,6 +125,14 @@ void schedule(void)
     unsigned long flags;
     prev = current;
     local_irq_save(flags); 
+    if (in_callback) {
+        printk("Must not call schedule() from a callback\n");
+        BUG();
+    }
+    if (flags) {
+        printk("Must not call schedule() with IRQs disabled\n");
+        BUG();
+    }
     list_for_each(iterator, &exited_threads)
     {
         thread = list_entry(iterator, struct thread, thread_list);