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SubjectRe: [PATCH v2 2/2] hvc_xen: implement multiconsole support
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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