Re: [PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of_xlate()

From: Robin Murphy
Date: Thu Oct 29 2020 - 09:51:28 EST


On 2020-10-29 13:19, yukuai (C) wrote:

On 2020/10/29 18:08, Robin Murphy wrote:
On 2020-10-29 09:22, Yu Kuai wrote:
If of_find_device_by_node() failed in rk_iommu_of_xlate(), null pointer
dereference will be triggered. Thus return error code if
of_find_device_by_node() failed.

How can that happen? (Given that ".suppress_bind_attrs = true")

Robin.

I'm not sure if that could happen...

My thought is that it's better to do such checking to aviod any possible
problem.

->of_xlate() is only invoked on the specific set of ops returned by iommu_ops_from_fwnode(). In turn, iommu_ops_from_fwnode() will only return those ops if the driver has successfully probed and called iommu_register_device() with the relevant DT node. For the driver to have been able to probe at all, a platform device associated with that DT node must have been created, and therefore of_find_device_by_node() cannot fail.

If there ever were some problem serious enough to break that fundamental assumption, then I *want* these drivers to crash right here, with a nice clear stack trace to start debugging from. So no, I firmly disagree that adding redundant code, which will never do anything except attempt to paper over catastrophic memory corruption, is "better". Sorry :)

Robin.