linux-kernel - Re: [PATCH v2 02/13] xen/pvcalls: connect to the backend

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Date:   Mon, 31 Jul 2017 14:55:21 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org,
        jgross@...e.com, Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v2 02/13] xen/pvcalls: connect to the backend

On Thu, 27 Jul 2017, Boris Ostrovsky wrote:
> >>>   static int pvcalls_front_probe(struct xenbus_device *dev,
> >>>   			  const struct xenbus_device_id *id)
> >>>   {
> >>> +	int ret = -EFAULT, evtchn, ref = -1, i;
> >>> +	unsigned int max_page_order, function_calls, len;
> >>> +	char *versions;
> >>> +	grant_ref_t gref_head = 0;
> >>> +	struct xenbus_transaction xbt;
> >>> +	struct pvcalls_bedata *bedata = NULL;
> >>> +	struct xen_pvcalls_sring *sring;
> >>> +
> >>> +	if (pvcalls_front_dev != NULL) {
> >>> +		dev_err(&dev->dev, "only one PV Calls connection
> >>> supported\n");
> >>> +		return -EINVAL;
> >>> +	}
> >>> +
> >>> +	versions = xenbus_read(XBT_NIL, dev->otherend, "versions", &len);
> >>> +	if (!len)
> >>> +		return -EINVAL;
> >>> +	if (strcmp(versions, "1")) {
> >>> +		kfree(versions);
> >>> +		return -EINVAL;
> >>> +	}
> >>> +	kfree(versions);
> >>> +	ret = xenbus_scanf(XBT_NIL, dev->otherend,
> >>> +			   "max-page-order", "%u", &max_page_order);
> >>> +	if (ret <= 0)
> >>> +		return -ENODEV;
> >>> +	if (max_page_order < RING_ORDER)
> >>> +		return -ENODEV;
> >>> +	ret = xenbus_scanf(XBT_NIL, dev->otherend,
> >>> +			   "function-calls", "%u", &function_calls);
> >>> +	if (ret <= 0 || function_calls != 1)
> >>> +		return -ENODEV;
> >>> +	pr_info("%s max-page-order is %u\n", __func__, max_page_order);
> >>> +
> >>> +	bedata = kzalloc(sizeof(struct pvcalls_bedata), GFP_KERNEL);
> >>> +	if (!bedata)
> >>> +		return -ENOMEM;
> >>> +
> >>> +	init_waitqueue_head(&bedata->inflight_req);
> >>> +	for (i = 0; i < PVCALLS_NR_REQ_PER_RING; i++)
> >>> +		bedata->rsp[i].req_id = PVCALLS_INVALID_ID;
> >>> +
> >>> +	sring = (struct xen_pvcalls_sring *) __get_free_page(GFP_KERNEL |
> >>> +							     __GFP_ZERO);
> >>> +	if (!sring)
> >>> +		goto error;
> >>> +	SHARED_RING_INIT(sring);
> >>> +	FRONT_RING_INIT(&bedata->ring, sring, XEN_PAGE_SIZE);
> >>> +
> >>> +	ret = xenbus_alloc_evtchn(dev, &evtchn);
> >>> +	if (ret)
> >>> +		goto error;
> >>> +
> >>> +	bedata->irq = bind_evtchn_to_irqhandler(evtchn,
> >>> +						pvcalls_front_event_handler,
> >>> +						0, "pvcalls-frontend", dev);
> >>> +	if (bedata->irq < 0) {
> >>> +		ret = bedata->irq;
> >>> +		goto error;
> >>> +	}
> >>> +
> >>> +	ret = gnttab_alloc_grant_references(1, &gref_head);
> >>> +	if (ret < 0)
> >>> +		goto error;
> >>> +	bedata->ref = ref = gnttab_claim_grant_reference(&gref_head);
> >> Is ref really needed?
> > No, I'll remove it
> >
> >
> >>> +	if (ref < 0)
> >>> +		goto error;
> >>> +	gnttab_grant_foreign_access_ref(ref, dev->otherend_id,
> >>> +					virt_to_gfn((void *)sring), 0);
> >>> +
> >>> + again:
> >>> +	ret = xenbus_transaction_start(&xbt);
> >>> +	if (ret) {
> >>> +		xenbus_dev_fatal(dev, ret, "starting transaction");
> >>> +		goto error;
> >>> +	}
> >>> +	ret = xenbus_printf(xbt, dev->nodename, "version", "%u", 1);
> >>> +	if (ret)
> >>> +		goto error_xenbus;
> >>> +	ret = xenbus_printf(xbt, dev->nodename, "ring-ref", "%d", ref);
> >>> +	if (ret)
> >>> +		goto error_xenbus;
> >>> +	ret = xenbus_printf(xbt, dev->nodename, "port", "%u",
> >>> +			    evtchn);
> >>> +	if (ret)
> >>> +		goto error_xenbus;
> >>> +	ret = xenbus_transaction_end(xbt, 0);
> >>> +	if (ret) {
> >>> +		if (ret == -EAGAIN)
> >>> +			goto again;
> >>> +		xenbus_dev_fatal(dev, ret, "completing transaction");
> >>> +		goto error;
> >>> +	}
> >>> +
> >>> +	INIT_LIST_HEAD(&bedata->socket_mappings);
> >>> +	INIT_LIST_HEAD(&bedata->socketpass_mappings);
> >>> +	spin_lock_init(&bedata->pvcallss_lock);
> >>> +	dev_set_drvdata(&dev->dev, bedata);
> >>> +	pvcalls_front_dev = dev;
> >>> +	xenbus_switch_state(dev, XenbusStateInitialised);
> >>> +
> >>>   	return 0;
> >>> +
> >>> + error_xenbus:
> >>> +	xenbus_transaction_end(xbt, 1);
> >>> +	xenbus_dev_fatal(dev, ret, "writing xenstore");
> >>> + error:
> >>> +	pvcalls_front_remove(dev);
> >> I think patch 12 (where you implement cleanup) could be moved before this one.
> > I'll move the patch
> >
> >
> >> I also think you are leaking bedata on error paths.
> > bedata is freed by pvcalls_front_remove (kfree(bedata)), why do you say
> > so?
> 
> bedata there is read from dev_get_drvdata() and here you assign drvdata
> at the very end.
> 
> Come think of it, pvcalls_front_remove() should probably first check
> whether bedata is valid. Or drvdata should be assigned right away in
> this routine, before any 'got error/error_xenbus'.

Yes, I'll do that