linux-kernel - Re: [PATCH v10 1/7] PCI: initialize and release SR-IOV capability

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Date:	Fri, 6 Mar 2009 18:38:45 -0800
From:	Greg KH <greg@...ah.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Yu Zhao <yu.zhao@...el.com>, jbarnes@...tuousgeek.org,
	linux-pci@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, "Randy.Dunlap" <rdunlap@...otime.net>
Subject: Re: [PATCH v10 1/7] PCI: initialize and release SR-IOV capability

On Fri, Mar 06, 2009 at 01:08:10PM -0700, Matthew Wilcox wrote:
> On Fri, Feb 20, 2009 at 02:54:42PM +0800, Yu Zhao wrote:
> > +	list_for_each_entry(pdev, &dev->bus->devices, bus_list)
> > +		if (pdev->sriov)
> > +			break;
> > +	if (list_empty(&dev->bus->devices) || !pdev->sriov)
> > +		pdev = NULL;
> > +	ctrl = 0;
> > +	if (!pdev && pci_ari_enabled(dev->bus))
> > +		ctrl |= PCI_SRIOV_CTRL_ARI;
> > +
> 
> I don't like this loop.  At the end of a list_for_each_entry() loop,
> pdev will not be pointing at a pci_device, it'll be pointing to some
> offset from &dev->bus->devices.  So checking pdev->sriov at this point
> is really, really bad.  I would prefer to see something like this:
> 
>         ctrl = 0;
>         list_for_each_entry(pdev, &dev->bus->devices, bus_list) {
>                 if (pdev->sriov)
>                         goto ari_enabled;
>         }
> 
>         if (pci_ari_enabled(dev->bus))
>                 ctrl = PCI_SRIOV_CTRL_ARI;
>  ari_enabled:
>         pci_write_config_word(dev, pos + PCI_SRIOV_CTRL, ctrl);

No, please use bus_for_each_dev() instead, or bus_find_device(), don't
walk the bus list by hand.  I'm kind of surprised that even builds.  Hm,
in looking at the 2.6.29-rc kernels, I notice it will not even build at
all, you are now forced to use those functions, which is good.

Has anyone even tried to build this patch recently?

thanks,

greg k-h
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