Re: 3.16rc3 multiplatform, Armada 370 and IOMMU: unbootable kernel

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Sat, Jul 05, 2014 at 12:03:08PM -0300, Ezequiel Garcia wrote:
> After following Gregory's stacktrace (also reproduced here):
> 
> [<c02451f8>] (iommu_bus_notifier) from [<c00512e8>] (notifier_call_chain+0x64/0x9c)
> [<c00512e8>] (notifier_call_chain) from [<c00514cc>] (__blocking_notifier_call_chain+0x40/0x58)
> [<c00514cc>] (__blocking_notifier_call_chain) from [<c00514f8>] (blocking_notifier_call_chain+0x14/0x1c)
> [<c00514f8>] (blocking_notifier_call_chain) from [<c01d225c>] (device_add+0x424/0x524)
> [<c01d225c>] (device_add) from [<c0186d90>] (pci_device_add+0xec/0x110)
> [<c0186d90>] (pci_device_add) from [<c0186e54>] (pci_scan_single_device+0xa0/0xac)
> 
> I added a few printks and found that the problem is that the iommu_bus_notifier is
> called for the 'pci' bus type, which has a null iommu_ops.
> 
> On 04 Jul 10:47 AM, Laurent Pinchart wrote:
> [..]
> > 
> > We need a quick fix for v3.16, ...
> 
> Therefore, a quick fix would be to simply check for that:
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index e5555fc..b712cb2 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -536,6 +536,9 @@ static int iommu_bus_notifier(struct notifier_block *nb,
>         struct iommu_group *group;
>         unsigned long group_action = 0;
>  
> +       if (!ops)
> +               return 0;
> +
>         /*
>          * ADD/DEL call into iommu driver ops if provided, which may
>          * result in ADD/DEL notifiers to group->notifier
> 
> This (nasty workaround?) patch makes the problem go away.
> 
> [..]
> > > So it also boot well in 3.15 and then failed in 3.16-rc3. I hope it will
> > > help the developers of the OMAP IOMMU driver to fix it.
> > 
> > Thank you. I've had a look at the OMAP IOMMU driver changes between v3.15 and 
> > v3.16-rc3, and didn't find at first sight any change that could explain the 
> > crash.
> > 
> > 286f600 iommu/omap: Fix map protection value handling
> > 67b779d iommu/omap: Remove comment about supporting single page mappings only
> > f7129a0 iommu/omap: Fix 'no page for' debug message in flush_iotlb_page()
> > 5acc97d iommu/omap: Move to_iommu definition from omap-iopgtable.h
> > 2ac6133 iommu/omap: Remove omap_iommu_domain_has_cap() function
> > d760e3e iommu/omap: Correct init value of iotlb_entry valid field
> > 
> > Could you try reverting those changes and retest ? If the problem doesn't 
> > disappear, we'll need to look somewhere else.
> > 
> 
> I reverted the above commits but nothing changed. I'm far from being an expert,
> but it sounds odd to have this bus notifier (that got registered for the
> platform bus type) called by a pci bus type.

Why wouldn't the PCI bus set this up for its devices?  Are you
"assuming" you know the bus type and that's the issue?

I see the a number of different places this is being initialized for the
pci bus.

Ah, look at drivers/iommu/fsl_pamu_domain.c, odds are, it shouldn't be
doing that logic in the pamu_domain_init() code, using the same bus ops
for different bus types, that's ripe for major problems...

thanks,

greg k-h