Re: [PATCH v2 1/1] cxl/mem: Fix no cxl_nvd during pmem region auto-assembing

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

Li Ming wrote:
> When CXL subsystem is auto-assembling a pmem region during cxl
> endpoint port probing, always hit below calltrack.
> 
>  BUG: kernel NULL pointer dereference, address: 0000000000000078
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  RIP: 0010:cxl_pmem_region_probe+0x22e/0x360 [cxl_pmem]
>  Call Trace:
>   <TASK>
>   ? __die+0x24/0x70
>   ? page_fault_oops+0x82/0x160
>   ? do_user_addr_fault+0x65/0x6b0
>   ? exc_page_fault+0x7d/0x170
>   ? asm_exc_page_fault+0x26/0x30
>   ? cxl_pmem_region_probe+0x22e/0x360 [cxl_pmem]
>   ? cxl_pmem_region_probe+0x1ac/0x360 [cxl_pmem]
>   cxl_bus_probe+0x1b/0x60 [cxl_core]
>   really_probe+0x173/0x410
>   ? __pfx___device_attach_driver+0x10/0x10
>   __driver_probe_device+0x80/0x170
>   driver_probe_device+0x1e/0x90
>   __device_attach_driver+0x90/0x120
>   bus_for_each_drv+0x84/0xe0
>   __device_attach+0xbc/0x1f0
>   bus_probe_device+0x90/0xa0
>   device_add+0x51c/0x710
>   devm_cxl_add_pmem_region+0x1b5/0x380 [cxl_core]
>   cxl_bus_probe+0x1b/0x60 [cxl_core]
> 
> Because the cxl_nvd of the memdev is necessary during pmem region
> probing, but the cxl_nvd can be registered only after endpoint port
> probing done, that is a collision dependency, so adjust the sequence
> between cxl_nvd registration and adding endpoint port to guarantee there
> is a cxl_nvd in memdev during the pmem region auto-assembling.
> 
> Fixes: f17b558d6663 ("cxl/pmem: Refactor nvdimm device registration, delete the workqueue")
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Li Ming <ming4.li@intel.com>

Looks good to me:

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