more defensive programming

1133b215 · rsc · f7017212 · 1133b215
--- a/proc.c
+++ b/proc.c
@@ -371,7 +371,9 @@ proc_wait(void)
    havekids = 0;
    for(i = 0; i < NPROC; i++){
      p = &proc[i];
-      if(p->state != UNUSED && p->ppid == cp->pid){
+      if(p->state == UNUSED)
+        continue;
+      if(p->ppid == cp->pid){
        if(p->state == ZOMBIE){
          // Found one.
          kfree(p->mem, p->sz);
@@ -379,6 +381,7 @@ proc_wait(void)
          pid = p->pid;
          p->state = UNUSED;
          p->pid = 0;
+          p->ppid = 0;
          release(&proc_table_lock);
          return pid;
        }