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

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Message-ID: <20110406152552.GU23633@amd.com>
Date:	Wed, 6 Apr 2011 17:25:52 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Greg Kroah-Hartman <gregkh@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	"Xu, Andiry" <Andiry.Xu@....com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>
Subject: Re: [PATCH] USB host: Fix lockdep warning in AMD PLL quirk

On Wed, Apr 06, 2011 at 11:16:07AM -0400, Alan Stern wrote:
> On Wed, 6 Apr 2011, Joerg Roedel wrote:
> >  	amd_chipset.probe_count++;
> >  	/* probe only once */
> >  	if (amd_chipset.probe_count > 1) {
> >  		spin_unlock_irqrestore(&amd_lock, flags);
> >  		return amd_chipset.probe_result;
> >  	}
> 
> The counter really should be a bool: Has the chipset already been
> probed or not?  After all, nobody cares how many times this routine was 
> called.

The quirk function needs a re-structuring anyway. The code-path is not
very straight-forward and readable. But for this fix I tried to keep the
changes small.

> 
> > +	spin_unlock_irqrestore(&amd_lock, flags);
> 
> This code now contains a bug: You incremented the probe_count _before_
> doing the probe.  If another thread calls this routine right now, it
> will get an incorrect result.
> 
> Fixing this up should be fairly easy.

Okay, I will do. Thanks for the feedback.

	Joerg

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