Re: [PATCH] libnvdimm: Let revalidate_disk() revalidate region read-only

[Dan Williams]

On Mon, Mar 8, 2021 at 11:31 PM Christoph Hellwig <hch@xxxxxx> wrote:
>
> On Mon, Mar 08, 2021 at 10:54:22PM -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
> > revalidate_disk() to clear 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.
>
> I've just resent my series to kill of ->revalidate_disk for good, so this
> obvious makes me a little unhappy.  Given that ->revalidate_disk
> only ends up beeing called from the same path that ->open is called,
> why can't you just hook this up from the open method?
>
> Also any reason the sysfs attribute can't just directly propagate the
> information to the disk?

I should have assumed that revalidate_disk() was on the chopping
block. Let me take a look at just propagating from the region update
down to all affected disks. There's already a notification path for
regions to communicate badblocks, should be straightforward to reuse
for read-only updates.