linux-kernel - Re: oops in pci_acs_path

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Date:	Fri, 03 Aug 2012 15:52:13 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: oops in pci_acs_path_enabled

On Fri, 2012-08-03 at 15:12 -0600, David Ahern wrote:
> 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.

Is this the chunk that's causing the oops?

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 7469b53..27d8c97 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4133,6 +4133,7 @@ static int intel_iommu_add_device(struct device *dev)
                                          PCI_DEVFN(PCI_SLOT(dma_pdev->devfn),
                                          0)));
 
+#if 0
        while (!pci_is_root_bus(dma_pdev->bus)) {
                if (pci_acs_path_enabled(dma_pdev->bus->self,
                                         NULL, REQ_ACS_FLAGS))
@@ -4140,6 +4141,7 @@ static int intel_iommu_add_device(struct device *dev)
 
                swap_pci_ref(&dma_pdev, pci_dev_get(dma_pdev->bus->self));
        }
+#endif
 
        group = iommu_group_get(&dma_pdev->dev);
        pci_dev_put(dma_pdev);


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