linux-kernel - Re: [PATCH -v2] pci: Check bridge resources after resource allocation.

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Date:	Mon, 16 May 2011 20:52:33 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Ram Pai <linuxram@...ibm.com>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH -v2] pci: Check bridge resources after resource
 allocation.

On Mon, 16 May 2011 15:36:21 -0700
Ram Pai <linuxram@...ibm.com> wrote:

> On Mon, May 16, 2011 at 01:55:38PM -0700, Yinghai Lu wrote:
> > On 05/16/2011 12:59 AM, Ram Pai wrote:
> > > On Fri, May 13, 2011 at 06:06:17PM -0700, Yinghai Lu wrote:
> > >> On 05/12/2011 12:34 PM, Jesse Barnes wrote:
> > >>> On Thu, 12 May 2011 12:18:43 -0700
> > >>> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > >>>
> > >>>> On Thu, May 12, 2011 at 11:37 AM, Jesse Barnes
> > >>>> <jbarnes@...tuousgeek.org> wrote:
> > >>>>>
> > >>>>> Linus, I don't have anything else queued up, so you may as
> > >>>>> well take this one directly if you want it in 2.6.39.  It's a
> > >>>>> regression fix, but resource changes always make me nervous.
> > >>>>> Alternately, I could put it into 2.6.40 instead, the backport
> > >>>>> to 2.6.39.x if it survives until 2.6.40-rc2 or so...
> > >>>>
> > >>>> Considering the trouble resource allocation always ends up
> > >>>> being, I'd almost prefer that "mark it for stable and put it
> > >>>> in the 2.6.40 queue".
> > >>>>
> > >>>> Afaik this problem hasn't actually hit any "normal" users, has
> > >>>> it? So ...
> > >>>
> > >>> Sounds good, thanks.  Yeah I don't think it's hit anyone but
> > >>> Yinghai (at least I don't know of any other reports).
> > >>>
> > >>
> > >> please check this one, it should be safe for 2.6.39 ?
> > > 
> > >>  	size0 = calculate_iosize(size, min_size, size1,
> > >>  			resource_size(b_res), 4096);
> > >> -	size1 = !add_size? size0:
> > >> +	size1 = (!add_head || (add_head && !add_size)) ? size0 :
> > >>  		calculate_iosize(size, min_size+add_size, size1,
> > >>  			resource_size(b_res), 4096);
> > > 
> > > This solves the problem you encountered.
> > > 
> > > But, I think, it still does not fix the following scenario:
> > > 
> > > adjust_resource() failing to allocate additional resource to a
> > > hotplug bridge that has no children. In this case  ->flags of
> > > that 'struct resource' continues to be set even when no resource
> > > is allocated to that hot-plug bridge.
> > > 
> > that case: requested_size will be 0, but add_size will not be zero.
> > 
> > res->flags is not cleared in pbus_size_xx, so it will be put into
> > head. so it will go through first path.
> > ...
> >                 if (!resource_size(res) && add_size) {
> >                          res->end = res->start + add_size - 1;
> >                          if(pci_assign_resource(list->dev, idx))
> >                                 reset_resource(res);
> >                 } else if (add_size) {
> >                         adjust_resource(res, res->start,
> >                                 resource_size(res) + add_size);
> >                 }
> > 
> > and if it fails to get assign, the flags will get clear in
> > reset_resource.
> > 
> > so it should be ok. and testing in one my setup show those flags
> > get clear correctly and does not emit any warning.
> 
> 
> Ack. You are right.
> 
> Linus/Jesse:  can we consider this patch for 2.6.39? It is the
> simplest fix to the problem.
> 
> Reviewed-by: Ram Pai <linuxram@...ibm.com>

I'll queue it up for 2.6.40 with stable cc'd.

Thanks,
Jesse
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