a few nits

passes all tests on two-processor smp

bio.c

@@ -109,7 +109,6 @@ bread(uint dev, uint sector)
 void
 bwrite(struct buf *b)
 {
-  cprintf("bwrite sector %d\n", b->sector);
   if((b->flags & B_BUSY) == 0)
     panic("bwrite");
   b->flags |= B_DIRTY;

exec.c

@@ -102,7 +102,7 @@ exec(char *path, char **argv)
   return 0;
 
  bad:
-  freevm(pgdir);
+  if (pgdir) freevm(pgdir);
   iunlockput(ip);
   return -1;
 }

kalloc.c

@@ -111,8 +111,6 @@ kalloc(int n)
     }
   }
   release(&kmem.lock);
-
-  cprintf("kalloc: out of memory\n");
   return 0;
 }