Re: git-latest: kernel oops in IOMMU setup

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Dirk Hohndel wrote:
On Sat, 10 Jan 2009 00:16:22 +0800
"Zhao, Yu" <yu.zhao@xxxxxxxxx> wrote:

Dirk Hohndel wrote:
On Fri, 9 Jan 2009 14:53:14 +0800
"Han, Weidong" <weidong.han@xxxxxxxxx> wrote:

Dirk Hohndel wrote:
On Thu, 8 Jan 2009 18:05:15 -0800
Dirk Hohndel <hohndel@xxxxxxxxxxxxx> wrote:

On Fri, 9 Jan 2009 08:58:46 +0800 "Han, Weidong"

I updated to Linus' latest git (as your description made me
wonder if the async stuff might play a role here). I still get
an oops - but at a different spot and the system no longer hangs
- it partly recovers (but things aren't too well - for example
my USB keyboard / mouse don't work anymore).
Spoke too soon. Rebooted and had the same hard lockup again. This
time I had my camera within reach, so here's the trace:

device_to_iommu+0x33/0x73
domain_context_mapping_one+0x37/0x335
domain_context_mapping+0x25/0xa7
iommu_prepare_identity+0xd7/0xf3
intel_iommu_init+0x4e4/0x8f3
? mutex_lock
? sysctl_net_init
? pci_iommu_init
pci_iommu_init

I also have stack, code and register values. Let me know if you
need them. Or I can just post the picture :-)

Again, very latest git tree, VT-d enabled.

/D
I tried latest git tree, it works for me. Above call trace looks
right.
Spent some more time reading the code. Can't quite claim to
understand all of it, yet, but I notice that most everywhere else
drhd->devices[i] is checked to be != NULL before it is accessed.
Why is it safe not to do that in device_to_iommu()?

Would the patch below be a valid fix? It stops my system from
hanging at boot. But I wonder if there is an assertion that if
drhd->ignored is 0 then drhd->devices[0..drhd->device_cnt] is known
to be != NULL and therefore this test is just hiding a bug
somewhere else...

/D

Signed-off-by: Dirk Hohndel <hohndel@xxxxxxxxxxxxxxx>
---
 drivers/pci/intel-iommu.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 235fb7a..3dfecb2 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -438,7 +438,8 @@ static struct intel_iommu *device_to_iommu(u8
bus, u8 devfn) continue;
for (i = 0; i < drhd->devices_cnt; i++)
-			if (drhd->devices[i]->bus->number == bus &&
+			if (drhd->devices[i] &&
+			    drhd->devices[i]->bus->number == bus &&
 			    drhd->devices[i]->devfn == devfn)
 				return drhd->iommu;
Did you see following in the kernel message?
                 printk(KERN_WARNING PREFIX
                 "Device scope device [%04x:%02x:%02x.%02x] not
found\n", segment, scope->bus, path->dev, path->fn);

If yes, then
		Acked-by: Yu Zhao <yu.zhao@xxxxxxxxx>

Yes,

DMAR: Device scope device [0000:00:03:02] not found
DMAR: Device scope device [0000:00:03:02] not found
DMAR: Device scope device [0000:00:03:03] not found
DMAR: Device scope device [0000:00:03:03] not found

The laptop has a nasty bios, try to update it if you want to get rid of these noises... assuming you are luck enough :-)
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