linux-kernel - Re: [pci] pci/mrst: Detect loops when reading fixed BAR cap.

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Date:	Fri, 16 Jul 2010 10:47:23 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [pci] pci/mrst:  Detect loops when reading fixed BAR cap.

On 07/16/2010 10:43 AM, Bjorn Helgaas wrote:
> On Wednesday, July 14, 2010 11:02:03 am Ben Greear wrote:
>> The mrst logic introduced in 2.6.33-rc8 in commit
>> a712ffbc199849364c46e9112b93b66de08e2c26 causes boot
>> to hang on at least this platform:
>>
>> Intel E5405 CPU
>> System Information
>> 	Manufacturer: Supermicro
>> 	Product Name: X7DBU
>>
>> The cause of the hang is that pci_cap points to itself
>> as the next capability, putting the fixed_bar_cap into
>> an endless loop.
>>
>> This patch detects the loop, prints a warning, and
>> continues on with useful work.  This strategy was
>> suggested by Robert Hancock<hancockrwd@...il.com>
>>
>> This should be a candidate for 2.6.34.y as well.
>>
>> Signed-off-by: Ben Greear<greearb@...delatech.com>
>> ---
>> :100644 100644 1cdc02c... 9535ba9... M	arch/x86/pci/mrst.c
>>   arch/x86/pci/mrst.c |   11 +++++++++++
>>   1 files changed, 11 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/x86/pci/mrst.c b/arch/x86/pci/mrst.c
>> index 1cdc02c..9535ba9 100644
>> --- a/arch/x86/pci/mrst.c
>> +++ b/arch/x86/pci/mrst.c
>> @@ -76,6 +76,17 @@ static int fixed_bar_cap(struct pci_bus *bus, unsigned int devfn)
>>   				return pos;
>>   		}
>>
>> +		if ((pcie_cap>>  20) == 0)
>> +			break;
>> +		
>> +		if ((pcie_cap>>  20)<= pos) {
>> +			printk(KERN_WARNING "WARNING: mrst:  detected loop"
>> +			       " when searching for fixed BAR cap, previous"
>> +			       " position: 0x%x new position: 0x%x"
>> +			       " bus-number: %i  devfn: %i\n",
>> +			       pos, pcie_cap>>  20, bus->number, devfn);
>
> Can you use dev_warn() here to print the device info in the
> standard way?

There seems to be a different way to do this.  Some of the folks who
understand this better are working on a patch (I tested something based
on HPA's suggestions and it fixed my problem at least.)

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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