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

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Message-ID: <Pine.LNX.4.44L0.1104071050270.2147-100000@iolanthe.rowland.org>
Date:	Thu, 7 Apr 2011 11:01:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Roedel, Joerg" <Joerg.Roedel@....com>
cc:	"Xu, Andiry" <Andiry.Xu@....com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.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 Thu, 7 Apr 2011, Roedel, Joerg wrote:

> So we could access the data structure without any locks if we want using
> atomic_t for the probe_count and isoc_reqs members. But as I've seen
> meanwhile the lock still needs to protect the access to the hardware in
> the usb_amd_quirk_pll() function.
> So its probably not worth the work, what do you think?

You might as well use the spinlock.

However, is there a good reason to zero out the amd_chipset members in
usb_amd_dev_put()?  Can these things be added and removed dynamically?  
If they can't then the data should remain valid indefinitely once it
has been probed, and you could call pci_dev_put() at the end of
usb_amd_find_chipset_info().

And if they can, is it valid to call pci_dev_put() in usb_amd_dev_put()  
while holding a spinlock?  You might want to move those calls to the
end of the function.

Alan Stern

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