Re: git-latest: kernel oops in IOMMU setup

[Zhao, Yu]

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>
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