linux-kernel - Re: [PATCH] PCI: Fix racing for pci device removing via sysfs

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Date:	Mon, 29 Apr 2013 14:32:15 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Gu Zheng <guz.fnst@...fujitsu.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: Fix racing for pci device removing via sysfs

On Mon, Apr 29, 2013 at 02:23:50PM -0700, Sarah Sharp wrote:
> On Mon, Apr 29, 2013 at 11:21:42AM -0700, Greg Kroah-Hartman wrote:
> > On Mon, Apr 29, 2013 at 11:15:50AM -0700, Bjorn Helgaas wrote:
> > > On Mon, Apr 29, 2013 at 08:19:10AM -0700, Yinghai Lu wrote:
> > > > On Mon, Apr 29, 2013 at 3:04 AM, Gu Zheng <guz.fnst@...fujitsu.com> wrote:
> > > > > On 04/27/2013 05:01 AM, Yinghai Lu wrote:
> > > > >> On Fri, Apr 26, 2013 at 1:53 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> > > > >>>
> > > > >>> You can't be serious.  This is a disgusting mess.  Checking a list
> > > > >>> pointer for LIST_POISON1?  As far as I'm concerned, this is a waste of
> > > > >>> my time.
> > > > 
> > > > looks like xhci is using that LIST_POISON1 ...
> > > > 
> > > Maybe my allergic reaction to your use of LIST_POISON1 is unjustified,
> > > but I am dubious about the idea that xhci was the only place that needed
> > > it before now, and we just happened to find one more place in PCI that
> > > needs it.  That doesn't make sense because good design patterns are used
> > > many times, not just once or twice.
> > > 
> > > I thought the whole point of the get/put scheme was that if we had a
> > > pointer to a correctly reference-counted object, we didn't need to check
> > > whether the object was still valid because the object remains valid until
> > > all the references are released.
> > 
> > You are correct, you shouldn't have to worry about that.  If you have to
> > do something like the LIST_POISON test, something is really wrong.
> 
> All right, I'll take a look at the xHCI code.  From a brief glance, both
> places that use LIST_POISON are handling a timed-out command.  The
> command handling in xHCI needs to get completely reworked anyway, due to
> other race conditions.
> 
> Were you suggesting I use the get/put scheme in the xHCI driver, or was
> that for Yinghai?

I thought for Yinghai, but really, no code should have to check that
type of thing, so if the xhci driver is, it shouldn't :)

thanks,

greg k-h
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