Re: [PATCH 1/2] cxl/region: Timeout auto region assembly waiting for endpoints

[<dan.j.williams@intel.com>]

Gregory Price wrote:
> On Fri, Jan 30, 2026 at 10:26:06AM -0800, dan.j.williams@intel.com wrote:
> > I do not see how we get into this situation. If dax_kmem comes up, then
> > there is nothing to clean up. Yes, these can race, but typical locking
> > should ensure full forward progress or cleanup.
> 
> yes as long as the watchdog checks for the region actually having come
> up or not before unbinding, it should be ok - but then it seems a little
> odd to push that to userland if the driver basically already has all
> that knowledge.

A couple observations:

1/ cxl-cli already knows that raw region unbind is problematic, hence
   the doom and gloom documentation around the --force option.

2/ The driver does not know the error recovery policy for region
   assembly. The mechanism being enabled is that, in the case of CXL
   assembly failing due to potential platform quirks, there is a chance
   that the default DAX fallback could recover operation.

If the fallback is always broken because of the insert_resource() in the
construct_region() path, then that constrained problem needs to be fixed
first. Once that mechanism is fixed the rest of this becomes a pure
policy problem and I argue is suitable for userspace to handle. The
incomplete region is the kernel telling the admin the unvarnished truth
about what it knows to about the CXL topology. Same as an incomplete
RAID array.