linux-kernel - Re: Regression with commit f9cde5f in 2.6.30-gitX

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Message-ID: <20090624155632.GB7239@us.ibm.com>
Date:	Wed, 24 Jun 2009 08:56:32 -0700
From:	Gary Hade <garyhade@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Larry Finger <Larry.Finger@...inger.net>,
	Gary Hade <garyhade@...ibm.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	x86 maintainers <x86@...nel.org>, Len Brown <lenb@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: Regression with commit f9cde5f in 2.6.30-gitX

On Wed, Jun 24, 2009 at 04:51:48PM +0200, Thomas Gleixner wrote:
> On Wed, 24 Jun 2009, Jaswinder Singh Rajput wrote:
> > Reported-by: Larry Finger <Larry.Finger@...inger.net>
> > Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@...il.com>
> > ---
> >  arch/x86/pci/acpi.c |   16 ++++++++++------
> >  1 files changed, 10 insertions(+), 6 deletions(-)
> > 
> > diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
> > index 16c3fda..0bc015f 100644
> > --- a/arch/x86/pci/acpi.c
> > +++ b/arch/x86/pci/acpi.c
> > @@ -69,6 +69,9 @@ setup_resource(struct acpi_resource *acpi_res, void *data)
> >  	struct resource *root;
> >  	int max_root_bus_resources = PCI_BUS_NUM_RESOURCES;
> >  
> > +	if (info->res_num >= PCI_BUS_NUM_RESOURCES)
> > +		return AE_OK;
> > +
> >  	status = resource_to_addr(acpi_res, &addr);
> >  	if (!ACPI_SUCCESS(status))
> >  		return AE_OK;
> > @@ -94,17 +97,18 @@ setup_resource(struct acpi_resource *acpi_res, void *data)
> >  	if (bus_has_transparent_bridge(info->bus))
> >  		max_root_bus_resources -= 3;
> >  	if (info->res_num >= max_root_bus_resources) {
> > -		printk(KERN_WARNING "PCI: Failed to allocate 0x%lx-0x%lx "
> > -			"from %s for %s due to _CRS returning more than "
> > -			"%d resource descriptors\n", (unsigned long) res->start,
> > -			(unsigned long) res->end, root->name, info->name,
> > -			max_root_bus_resources);
> > +		pr_warning("PCI: Failed to allocate 0x%lx-0x%lx "
> > +			   "from %s for %s due to _CRS returning more than "
> > +			   "%d resource descriptors\n",
> > +			   (unsigned long)res->start, (unsigned long)res->end,
> > +			   root->name, info->name, max_root_bus_resources);
> 
> Can you please avoid mixing cleanup patches with bug fixes ? I almost
> did not see the line below.
> 
> > +		info->bus->resource[info->res_num] = res;
> 
> Storing the resource in defeats the purpose of the original patch,
> which makes sure that we do _NOT_ use the last 3 slots of the resource
> array for a root bus with a transparent bridge.
> 
> >  		info->res_num++;
> 
> This is the real bug. info->res_num should not be incremented when we
> run out of resources already.

This probably isn't needed but I don't think it is the cause of
the problem.  It is just counting the number of _CRS returned
resources and I believe subsequent visits to setup_resource()
for additional returned resources will generate the same warning
as it also would if the instruction were removed and no longer
being used to keep an accurate count.

I suspect that the resource array is simply not large enough
for that system (and possibly others) and will have to be made
larger by increasing PCI_BUS_NUM_RESOURCES.

Gary

-- 
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503  IBM T/L: 775-4503
garyhade@...ibm.com
http://www.ibm.com/linux/ltc

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