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

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Message-ID: <20110407075049.GV23633@amd.com>
Date:	Thu, 7 Apr 2011 09:50:49 +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:

> 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.
> 
> > +	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.

Hmm, we can get rid of the amd_lock completly if every thread uses the
following call-order:

	usb_amd_find_chipset_info();
	usb_amd_quirk_pll_enable();
	usb_amd_quirk_pll_disable();
	usb_amd_dev_put();

In that case we can just change the probe_count and isoc_reqs into
atomic_t with some care and should be fine, no?
Problem is that I don't know if the above call-order is guaranteed.

	Joerg

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