Re: [PATCH] resource: fix false warning in __request_region()

[dan.j.williams]

Akinobu Mita wrote:
> 2025年7月20日(日) 8:31 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>:
> >
> > On Sat, 19 Jul 2025 20:26:04 +0900 Akinobu Mita <akinobu.mita@xxxxxxxxx> wrote:
> >
> > > A warning is raised when __request_region() detects a conflict with a
> > > resource whose resource.desc is IORES_DESC_DEVICE_PRIVATE_MEMORY.
> > >
> > > But this warning is only valid for iomem_resources.
> > > The hmem device resource uses resource.desc as the numa node id, which can
> > > cause spurious warnings.
> > >
> > > This change fixes this by restricting the warning to only iomem_resource.
> > > This also adds a missing new line to the warning message.
> >
> > What are the circumstance which cause this warning?  Are real world
> > users hitting this?  If so, should we backport this fix into earlier
> > kernels?
> 
> This warning actually appeared on a machine with multiple cxl memory expanders.
> One of the NUMA node id is 6, which is the same as the value of
> IORES_DESC_DEVICE_PRIVATE_MEMORY.
> 
> In this environment it was just a spurious warning, but when I saw the warning
> I suspected a real problem so it's better to fix it.
> 
> Fixes: b926b7f3baec ("mm/resource: Move HMM pr_debug() deeper into
> resource code")

This should be:

Fixes: 7dab174e2e27 ("dax/hmem: Move hmem device registration to dax_hmem.ko")

...as that is the change that violates the assumptions of
__request_region().

You can add:

Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>