linux-kernel - Re: [RFC PATCH 1/5] pci/p2p: add a function to test peer to peer capability

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Date:   Tue, 29 Jan 2019 20:44:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     jglisse@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Christian Koenig <christian.koenig@....com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Jason Gunthorpe <jgg@...lanox.com>, linux-pci@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <jroedel@...e.de>,
        iommu@...ts.linux-foundation.org
Subject: Re: [RFC PATCH 1/5] pci/p2p: add a function to test peer to peer
 capability

On Tue, Jan 29, 2019 at 11:24:09AM -0700, Logan Gunthorpe wrote:
> 
> 
> On 2019-01-29 10:47 a.m., jglisse@...hat.com wrote:
> > +bool pci_test_p2p(struct device *devA, struct device *devB)
> > +{
> > +	struct pci_dev *pciA, *pciB;
> > +	bool ret;
> > +	int tmp;
> > +
> > +	/*
> > +	 * For now we only support PCIE peer to peer but other inter-connect
> > +	 * can be added.
> > +	 */
> > +	pciA = find_parent_pci_dev(devA);
> > +	pciB = find_parent_pci_dev(devB);
> > +	if (pciA == NULL || pciB == NULL) {
> > +		ret = false;
> > +		goto out;
> > +	}
> > +
> > +	tmp = upstream_bridge_distance(pciA, pciB, NULL);
> > +	ret = tmp < 0 ? false : true;
> > +
> > +out:
> > +	pci_dev_put(pciB);
> > +	pci_dev_put(pciA);
> > +	return false;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_test_p2p);
> 
> This function only ever returns false....

I guess it was nevr actually tested :(

I feel really worried about passing random 'struct device' pointers into
the PCI layer.  Are we _sure_ it can handle this properly?

thanks,

greg k-h