Re: [PATCH] CodingStyle: add some more error handling guidelines

Michael S. Tsirkin
2016-08-22T18:39:40Z

On Mon, Aug 22, 2016 at 09:31:40PM +0300, Dan Carpenter wrote:
>
> vhost_dev_set_owner() is an example of why come-from labels are
> bad style.
>
> devel/drivers/vhost/vhost.c
> 473 /* Caller should have device mutex */
> 474 long vhost_dev_set_owner(struct vhost_dev *dev)
> 475 {
> 476 struct task_struct *worker;
> 477 int err;
> 478
> 479 /* Is there an owner already? */
> 480 if (vhost_dev_has_owner(dev)) {
> 481 err = -EBUSY;
> 482 goto err_mm;
>
> What does goto err_mm do? It's actually a do-nothing goto. It would
> be easier to read as a direct return. Why is it called err_mm? Because
> originally the condition was:
>
> if (dev->mm) {
> err = -EBUSY;
> goto err_mm;
> }
>
> We've changed the code but didn't update the label so it's slightly
> confusing unless you know how vhost_dev_has_owner() is implemented.
>
> 483 }
> 484
> 485 /* No owner, become one */
> 486 dev->mm = get_task_mm(current);
> 487 worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
> 488 if (IS_ERR(worker)) {
> 489 err = PTR_ERR(worker);
> 490 goto err_worker;
> 491 }
> 492
> 493 dev->worker = worker;
> 494 wake_up_process(worker); /* avoid contributing to loadavg */
> 495
> 496 err = vhost_attach_cgroups(dev);
> 497 if (err)
> 498 goto err_cgroup;
> 499
> 500 err = vhost_dev_alloc_iovecs(dev);
> 501 if (err)
> 502 goto err_cgroup;
>
> This name doesn't make sense because it's a come-from label which is
> used twice. Some people do:
>
> if (err)
> goto err_iovecs;
>
> 503
> 504 return 0;

Right and the current CodingStyle text seems to discourage this.

> Then they add two labels here:
>
> err_iovecs:
> err_cgroup:
> kthread_stop(worker);

Definitely good points above, I'll fix them up.

> But if you base the label name on the label location then it makes
> sense. goto stop_kthread; goto err_mmput;.
>
> 505 err_cgroup:
> 506 kthread_stop(worker);
> 507 dev->worker = NULL;
> 508 err_worker:
> 509 if (dev->mm)
> 510 mmput(dev->mm);
> 511 dev->mm = NULL;
> 512 err_mm:
> 513 return err;
> 514 }
>
> regards,
> dan carpenter

OK, I'll consider this, thanks!

--
MST