linux-kernel - Re: [PATCH v5] USB host: Fix lockdep warning in AMD PLL quirk

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Date:	Mon, 11 Apr 2011 13:05:41 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
cc:	Borislav Petkov <bp@...en8.de>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	"Xu, Andiry" <Andiry.Xu@....com>,
	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] USB host: Fix lockdep warning in AMD PLL quirk

On Mon, 11 Apr 2011, Roedel, Joerg wrote:

> > > > > +		ret = amd_chipset.probe_result;
> > > > > +
> > > > > +		spin_unlock_irqrestore(&amd_lock, flags);
> > > > > +
> > > > > +		if (info.nb_dev)
> > > > > +			pci_dev_put(info.nb_dev);
> > > > > +		if (info.smbus_dev)
> > > > > +			pci_dev_put(info.smbus_dev);
> > > > > +
> > > > > +	} else {
> > > > > +		/* no race - commit the result */
> > > > > +		info.probe_count++;
> > > > 
> > > > This isn't right, because info.probe_count was initialized to 0.  Maybe 
> > > > amd_chipset.probe_count should be made into a separate variable, not a 
> > > > part of the structure, like amd_lock.
> > > 
> > > The purpose of the struct is structuring of data. In theory all of its
> > > members could be turned into global variables. The amd_lock is different
> > > because it does not only protect the struct but also access to the
> > > hardware while the quirk is applied/unapplied.
> > 
> > Do it however you prefer.  But as it stands now, the patch is wrong.
> 
> Hmm, I see how it can be done differently, but no real bug.

Never mind, you're right.  In the no-race case, the initial count is 
always going to be 0, and so incrementing info.probe_count is the right 
thing to do.

Alan Stern

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