cvs add spinlock.h

fix race in schedule()

Notes

@@ -126,3 +126,10 @@ in general, the table locks protect both free-ness and
 why can't i get a lock in console code?
   always triple fault
 lock code shouldn't call cprintf...
+ide_init doesn't work now?
+and IOAPIC: read from unsupported address
+  when running pre-empt user test
+  so maybe something wrong with clock interrupts
+  no! if one cpu holds lock w/ curproc0=,
+    then another cpu can take it, it looks like
+    a recursive acquire()

proc.c

@@ -148,7 +148,6 @@ scheduler(void)
 
     if(i < NPROC){
       np->state = RUNNING;
-      release(&proc_table_lock);
       break;
     }
 
@@ -159,6 +158,8 @@ scheduler(void)
   cpus[cpu()].lastproc = np;
   curproc[cpu()] = np;
 
+  release(&proc_table_lock);
+
   // h/w sets busy bit in TSS descriptor sometimes, and faults
   // if it's set in LTR. so clear tss descriptor busy bit.
   np->gdt[SEG_TSS].sd_type = STS_T32A;

spinlock.h

@@ -0,0 +1,6 @@
+struct spinlock {
+  unsigned int locked;
+  struct proc *p;
+  int count;
+  unsigned locker_pc;
+};

usertests.c

@@ -93,8 +93,8 @@ preempt()
 main()
 {
   puts("usertests starting\n");
-  pipe1();
-  //preempt();
+  //pipe1();
+  preempt();
 
   while(1)
     ;