Re: [PATCH 1/2] cxl/core: Set cxlmd->endpoint to NULL by default

[Gregory Price <gourry@gourry.net>]

On Mon, Feb 02, 2026 at 02:41:03PM +0000, Jonathan Cameron wrote:
> On Sun,  1 Feb 2026 17:30:01 +0800
> Li Ming <ming.li@zohomail.com> wrote:
> 
> > CXL testing environment can trigger following trace
> > 
> >  Oops: general protection fault, probably for non-canonical address 0xdffffc0000000092: 0000 [#1] SMP KASAN NOPTI
> >  KASAN: null-ptr-deref in range [0x0000000000000490-0x0000000000000497]
> >  RIP: 0010:cxl_dpa_to_region+0x105/0x1f0 [cxl_core]
> >  Call Trace:
> >   <TASK>
> >   cxl_event_trace_record+0xd1/0xa70 [cxl_core]
> >   __cxl_event_trace_record+0x12f/0x1e0 [cxl_core]
> >   cxl_mem_get_records_log+0x261/0x500 [cxl_core]
> >   cxl_mem_get_event_records+0x7c/0xc0 [cxl_core]
> >   cxl_mock_mem_probe+0xd38/0x1c60 [cxl_mock_mem]
> >   platform_probe+0x9d/0x130
> >   really_probe+0x1c8/0x960
> >   __driver_probe_device+0x187/0x3e0
> >   driver_probe_device+0x45/0x120
> >   __device_attach_driver+0x15d/0x280
> > 
> > commit 29317f8dc6ed ("cxl/mem: Introduce cxl_memdev_attach for CXL-dependent operation")
> > initializes cxlmd->endpoint to ERR_PTR(-ENXIO) in cxl_memdev_alloc().
> > However, cxl_dpa_to_region() treats a non-NULL cxlmd->endpoint as a
> > valid endpoint.
> > 
> > Across the CXL core, endpoint availability is generally determined by
> > checking whether it is NULL. Align with this convention by initializing
> > cxlmd->endpoint to NULL by default.
> 
> I had a look at whether it made sense to use use IS_ERR_OR_NULL() to check
> for validity of the endpoint, but it would be somewhat fiddly and I think
> you are correct that convention here seems to be NULL means not set.
> We don't need the error code.  One comment inline.
> 

doing validity checks on pointers by checking for null is a pretty
common convention kernel-wide, I would consider setting some structure's
value to an ERR_PTR to be the aberration.

So yeah, good catch

Reviewed-by: Gregory Price <gourry@gourry.net>

~Gregory