Re: [Xen-devel] [PATCH v2 2/2] hvc_xen: implement multiconsole support

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 27 Jan 2012, Konrad Rzeszutek Wilk wrote:
> > +static void xencons_disconnect_backend(struct xencons_info *info)
> > +{
> > +   if (info->irq > 0)
> > +           unbind_from_irqhandler(info->irq, NULL);
> > +   info->irq = 0;
> > +   if (info->evtchn > 0)
> > +           xenbus_free_evtchn(info->xbdev, info->evtchn);
> > +   info->evtchn = 0;
> > +   if (info->gntref > 0)
> > +           gnttab_free_grant_references(info->gntref);
> > +   info->gntref = 0;
> > +   if (info->hvc != NULL)
> > +           hvc_remove(info->hvc);
> > +   info->hvc = NULL;
> > +}
> > +
> > +static void xencons_free(struct xencons_info *info)
> > +{
> > +   xencons_disconnect_backend(info);
> > +   free_page((unsigned long)info->intf);
> > +   info->intf = NULL;
> > +   info->vtermno = 0;
> > +   kfree(info);
> > +}
> > +
> > +static int xencons_remove(struct xenbus_device *dev)
> > +{
> > +   struct xencons_info *info = dev_get_drvdata(&dev->dev);
> > +
> 
> I would say put
>       xencons_disconnect_backend(info)
> 
> here, that way it calls hvc_remove first, and then this would
> delete an "not-called" anymore structure.
> 
> > +   spin_lock(&xencons_lock);
> > +   list_del(&info->list);
> > +   spin_unlock(&xencons_lock);
> > +   xencons_free(info);
> 
> >     return 0;
> >  }
> >
> 
> .. snip..
> > +
> > +static const struct xenbus_device_id xencons_ids[] = {
> > +   { "console" },
> > +   { "" }
> > +};
> > +
> > +
> >  static void __exit xen_hvc_fini(void)
> >  {
> > -   if (hvc)
> > -           hvc_remove(hvc);
> > +   struct xencons_info *entry, *next;
> > +
> > +   if (list_empty(&xenconsoles))
> > +                   return;
> > +
> > +   spin_lock(&xencons_lock);
> 
> Take that spin-lock out.
> 
> > +   list_for_each_entry_safe(entry, next, &xenconsoles, list) {
> > +           list_del(&entry->list);
> > +           if (entry->xbdev)
> > +                   xencons_remove(entry->xbdev);
> 
> This guy deletes itself from the list..
> > +           else {
> > +                   if (entry->irq > 0)
> > +                           unbind_from_irqhandler(entry->irq, NULL);
> > +                   if (entry->hvc);
> > +                           hvc_remove(entry->hvc);
> > +                   kfree(entry);
> 
> ..but this one does not.  You could make xencons_remove just remove
> itself from the list and nothing else. Then rename it to 
> 'xencons_remove_itself' perhaps?
> 
> After that, introduce a new function 'xencons_delete' that would call
> xecons_disconnect_backend, xencons_remove_itself, and xencons_free?

Thanks for spotting the deadlock and the useful suggestions.
I have reworked the shutdown path a bit, making sure that we don't take
any locks twice and that we call hvc_remove before list_del (see next
version of the patch, to be posted soon).



> >  
> > +static struct xenbus_driver xencons_driver = {
> 
> This needs to be wrapped in the new macro that Jan prepared.
> DEFINE_XENBUS_DRIVER (73db144b58a32fc39733db6a7e1fe582072ad26a)

OK

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