linux-kernel - Re: oops in pci_acs_path

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Date:	Fri, 03 Aug 2012 15:12:23 -0600
From:	David Ahern <dsahern@...il.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: oops in pci_acs_path_enabled

On 8/3/12 2:21 PM, Alex Williamson wrote:
> On Fri, 2012-08-03 at 11:39 -0600, David Ahern wrote:
>> Hi Alex:
>>
>> Hitting an oops with 3.6-rc1. Backtrace from console attached. git blame
>> for the top function points to ad805758.
>
> Hey David,
>
> Hmm, what's special about your system?  I've got an 82576 here and the
> same path works fine.  Any way you can get the top of the oops message?
> Thanks,
>
> Alex
>

Dell R410 I believe. pair of 5620 processors. 3 overlapping screen shots 
attached. objdump on pci.o suggests the pdev is NULL:

/opt/sw/ahern/kernels/kernel.git/drivers/pci/pci.c:2454

         ret = pci_dev_specific_acs_enabled(pdev, acs_flags);
         if (ret >= 0)
                 return ret > 0;

         if (!pci_is_pcie(pdev))
     408a:       41 80 7c 24 4a 00       cmpb   $0x0,0x4a(%r12)
     4090:       74 e8                   je     407a <pci_acs_enabled+0x2a>


Perhaps this bug explains the larger the issue which is that device 
passthrough in 3.6-rc1 (0d7614f) is broken for me -- config field for 
the PCI device does not exist. e.g.,

pcilib: Cannot open /sys/bus/pci/devices/0000:06:10.0/config
lspci: Unable to read the standard configuration space header of device 
0000:06:10.0
pcilib: Cannot open /sys/bus/pci/devices/0000:06:10.0/config
lspci: Unable to read the standard configuration space header of device 
0000:06:10.0
failed to find vendor-product id for PCI id "06:10.0"
Failed to claim PCI device 06:10.0

git bisect points to:

783f157bc5a7fa30ee17b4099b27146bd1b68af4 is the first bad commit
commit 783f157bc5a7fa30ee17b4099b27146bd1b68af4
Author: Alex Williamson <alex.williamson@...hat.com>
Date:   Wed May 30 14:19:43 2012 -0600

     intel-iommu: Make use of DMA quirks and ACS checks in IOMMU groups

     Work around broken devices and adhere to ACS support when determining
     IOMMU grouping.

     Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
     Signed-off-by: Joerg Roedel <joerg.roedel@....com>

:040000 040000 83890398dabbf225fd0f5b3c8c3713a75b3fb5e1 
b674ce2ecb315393a8c6c1ac98b3796d5ba09708 M	drivers

I triggered the oops in a number of the bisect points as well -- in 
those cases the machine had to be power cycled.

David


Download attachment "oops1.png" of type "image/png" (42116 bytes)

Download attachment "oops2.png" of type "image/png" (40206 bytes)

Download attachment "oops3.png" of type "image/png" (39749 bytes)