On Thu, Apr 07, 2011 at 05:01:01AM -0400, Xu, Andiry wrote: > > -----Original Message----- > > From: Roedel, Joerg [mailto:Joerg.Roedel@xxxxxxx] > > Sent: Thursday, April 07, 2011 3:51 PM > > To: Alan Stern > > Cc: Greg Kroah-Hartman; Sarah Sharp; Xu, Andiry; linux-usb@xxxxxxxxxxxxxxx; > > linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxx > > 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(); > > > > The correct order is: > > usb_amd_find_chipset_info(); > usb_amd_quirk_pll_disable(); > usb_amd_quirk_pll_enable(); > usb_amd_dev_put(); > > The pair of pll disable and enable may be called for multiple times. 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? Regards, Joerg -- AMD Operating System Research Center Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
