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

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Date:	Mon, 16 May 2011 15:36:21 -0700
From:	Ram Pai <linuxram@...ibm.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.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, 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>

RP
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