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

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Message-ID: <4DD18F4A.5030208@kernel.org>
Date:	Mon, 16 May 2011 13:55:38 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Ram Pai <linuxram@...ibm.com>
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 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.

Thanks

Yinghai
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