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

[yukuai (C)]

On 2020/10/29 21:51, Robin Murphy wrote:
> 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 :)

Sounds reasonable, thanks for your explanation

Yu Kuai