linux-kernel - Re: [PATCH v4] USB host: Fix lockdep warning in AMD PLL quirk

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Date:	Fri, 8 Apr 2011 17:09:55 +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 v4] USB host: Fix lockdep warning in AMD PLL quirk

On Fri, Apr 08, 2011 at 10:52:59AM -0400, Alan Stern wrote:
> On Fri, 8 Apr 2011, Joerg Roedel wrote:
> > -	amd_chipset.probe_count++;
> >  	/* probe only once */
> > -	if (amd_chipset.probe_count > 1) {
> > +	if (amd_chipset.probe_count > 0) {
> 
> You need to increment probe_count here.

Argh, right.

> 
> >  		spin_unlock_irqrestore(&amd_lock, flags);
> >  		return amd_chipset.probe_result;
> >  	}
> > +	info = amd_chipset;
> 
> What's the point of this line?  You're just going to write over all the 
> data in info anyway, so it doesn't matter what amd_chipset contains.  A 
> memset would work just as well.

info is on-stack and needs to be initialized somehow because the
following code does not touch the whole data structure.

> 
> > @@ -284,8 +310,10 @@ EXPORT_SYMBOL_GPL(usb_amd_quirk_pll_enable);
> >  
> >  void usb_amd_dev_put(void)
> >  {
> > +	struct pci_dev *nb, *smbus;
> >  	unsigned long flags;
> >  
> > +
> 
> Why add an extra blank line?

Left-over from editing.

> 
> >  	spin_lock_irqsave(&amd_lock, flags);
> >  
> >  	amd_chipset.probe_count--;
> > @@ -294,20 +322,23 @@ void usb_amd_dev_put(void)
> >  		return;
> >  	}
> >  
> > -	if (amd_chipset.nb_dev) {
> > -		pci_dev_put(amd_chipset.nb_dev);
> > -		amd_chipset.nb_dev = NULL;
> > -	}
> > -	if (amd_chipset.smbus_dev) {
> > -		pci_dev_put(amd_chipset.smbus_dev);
> > -		amd_chipset.smbus_dev = NULL;
> > -	}
> > +	/* save them to pci_dev_put outside of spinlock */
> > +	nb    = amd_chipset.nb_dev;
> > +	smbus = amd_chipset.smbus_dev;
> > +
> > +	amd_chipset.nb_dev = NULL;
> > +	amd_chipset.smbus_dev = NULL;
> >  	amd_chipset.nb_type = 0;
> >  	amd_chipset.sb_type = 0;
> >  	amd_chipset.isoc_reqs = 0;
> >  	amd_chipset.probe_result = 0;
> 
> You could use memset instead.  However, in reality it shouldn't be
> necessary to set any of these things to 0.

Well, I left this code as it was before because this is meant as a fix
and I tried to keep it small. For a fix it is already really big...
But that can certainly be changed in a follow-on patch.

	Joerg

-- 
AMD Operating System Research Center

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Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632

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