Re: [PATCH v4 8/9] iommu: Remove unused argument in is_attach_deferred

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Mar 30, 2022 at 08:19:37PM +0300, Tony Lindgren wrote:

> > > __iommu_probe_device from probe_iommu_group+0x2c/0x38
> > > probe_iommu_group from bus_for_each_dev+0x74/0xbc
> > > bus_for_each_dev from bus_iommu_probe+0x34/0x2e8
> > > bus_iommu_probe from bus_set_iommu+0x80/0xc8
> > > bus_set_iommu from omap_iommu_init+0x88/0xcc
> > > omap_iommu_init from do_one_initcall+0x44/0x24c
> > > 
> > > Any ideas for a fix?
> > > 
> > > It would be good to fix this quickly so we don't end up with a broken
> > > v5.18-rc1..
> > > 
> > > For reference, this is mainline commit 41bb23e70b50 ("iommu: Remove unused
> > > argument in is_attach_deferred").
> > 
> > Are you confident in the bisection? I don't see how that commit could
> > NULL deref..
> 
> Oops sorry you're right, the breaking commit is a different patch, it's
> 3f6634d997db ("iommu: Use right way to retrieve iommu_ops") instead. I must
> have picked the wrong commit while testing.

That makes alot more sense
 
> > Can you find the code that is the NULL deref?
> 
> I can debug a bit more tomorrow.

Looks like omap's omap_iommu_probe_device() is buggy, it returns 0 on
error paths:

	num_iommus = of_property_count_elems_of_size(dev->of_node, "iommus",
						     sizeof(phandle));
	if (num_iommus < 0)
		return 0;

This function needs to return an errno -ENODEV

Otherwise it causes a NULL dev->iommu->iommu_dev and dev_iommu_ops() will
crash.

Jason