Re: [PATCH v2] cxl/region: Unregister the pmem region bridge on setup failure

[Alison Schofield <alison.schofield@intel.com>]

On Fri, Aug 28, 2026 at 05:06:55PM +0800, Guixin Liu wrote:
> 
> 
> 在 2026/8/13 05:42, Alison Schofield 写道:
> > On Wed, Aug 12, 2026 at 02:10:43PM +0800, Guixin Liu wrote:
> > 
> > About the subject line:
> > 
> > Do we unregister the bridge or do we unregister the pmem
> > region when the bridge is unboound?
> > 
> Unregister the pmem region, sorry for the confusing description.
> > > devm_cxl_add_pmem_region() publishes the cxl_pmem_region with device_add()
> > > and only afterwards, under the nvdimm bridge's device lock, arranges for
> > > its removal - and only if the bridge has a driver bound. If it does not,
> > > the function sets -ENXIO and leaves through err_bridge, which drops the
> > > reference this function took on the bridge and returns. The device that
> > > was just added has no owner at that point: no device_del(), no
> > > put_device(), and no devm action to do either later. The sibling failure,
> > > a devm_add_action_or_reset() that cannot allocate, is already covered,
> > > because devm_add_action_or_reset() runs cxlr_pmem_unregister() itself on
> > > that path.
> > > 
> > > An unbound bridge is a normal state, not an error state. The bridge is
> > > unbound whenever cxl_pmem is unloaded or its device is detached through
> > > sysfs, and a region can be probed in that window.
> > > 
> > > The added device then stays in sysfs, along with the reference it holds on
> > > the region, until the module is unloaded. cxlr->cxlr_pmem still points at
> > > it, and worse, the name is still taken: a later probe of the same region
> > > allocates a second cxl_pmem_region and fails in device_add() on the
> > > duplicate "pmem_region%d", so once this has happened the region can no
> > > longer be brought up at all.
> > Is above an observed behavior?  ie can you reproduce this, apply
> > the fix, see it go away?  That would be far more valuable than this
> > excessive narration as proof of repair.
> > 
> > More below...
> I'm so sorry, I thought that we should add cleanup in
> failure branch, but now I realize that this branch is never actually
> reached.
> 

I think the patch may still apply as-is, so before dropping it, please take a
look at this from the teardown side rather than the "cxl_pmem is not loaded" side.

cxl_acpi removal unbinds and deletes the bridge before the regions it serves. So,
a region probe that already found the bridge can reach that check after the bridge
is gone, set -ENXIO, and return leaving the just-added device with no owner.

If that is true (I'm not sure it is) then the fix stands and the changelog needs to
tell that story.


-- Alison


> Please ignore this patch, sorry again.
> 
> Best Regards,
> Guixin Liu
>