Re: [PATCH v2] libnvdimm: Notify disk drivers to revalidate region read-only

On Tue, 2021-03-09 at 17:43 -0800, Dan Williams wrote:

Previous kernels allowed the BLKROSET to override the disk's read-only
status. With that situation fixed the pmem driver needs to rely on
notification events to reevaluate the disk read-only status after the
host region has been marked read-write.

Recall that when libnvdimm determines that the persistent memory has
lost persistence (for example lack of energy to flush from DRAM to FLASH
on an NVDIMM-N device) it marks the region read-only, but that state can
be overridden by the user via:

   echo 0 > /sys/bus/nd/devices/regionX/read_only

...to date there is no notification that the region has restored
persistence, so the user override is the only recovery.

Fixes: 52f019d43c22 ("block: add a hard-readonly flag to struct gendisk")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <redacted>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Jens Axboe <axboe@kernel.dk>
Reported-by: kernel test robot <redacted>
Reported-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <redacted>
---
Changes since v1 [1]:
- Move from the sinking ship of revalidate_disk() to the local hotness
  of nd_pmem_notify() (hch).

[1]: http://lore.kernel.org/r/161527286194.446794.5215036039655765042.stgit@dwillia2-desk3.amr.corp.intel.com (local)

 drivers/nvdimm/bus.c         |   14 ++++++--------
 drivers/nvdimm/pmem.c        |   37 +++++++++++++++++++++++++++++++++----
 drivers/nvdimm/region_devs.c |    7 +++++++
 include/linux/nd.h           |    1 +
 4 files changed, 47 insertions(+), 12 deletions(-)

With the update to the unit test applied, and this, everything passes
for me. You can add:

Tested-by: Vishal Verma <vishal.l.verma@intel.com>