Re: [PATCH] libnvdimm, pmem: fix badblocks notification crash

The nd_pmem_notify() routine is called whenever an ARS (address-range-scrub) completes to communicate results to the per-namespace badblocks instances. When the namespace is in btt mode we crash because we do not allocate a struct pmem_device instance in that case. Resulting in the following crash signature:  BUG: unable to handle kernel NULL pointer dereference at 0000000000000030  IP: nd_pmem_notify+0x30/0xf0 [nd_pmem]  Call Trace:   nd_device_notify+0x40/0x50   child_notify+0x10/0x20   device_for_each_child+0x50/0x90   nd_region_notify+0x20/0x30   nd_device_notify+0x40/0x50   nvdimm_region_notify+0x27/0x30   acpi_nfit_scrub+0x341/0x590 [nfit]   process_one_work+0x197/0x450   worker_thread+0x4e/0x4a0   kthread+0x109/0x140 Given that we don't even populate the btt badblocks instance, just return early and skip the device to region lookup.