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

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Date:   Tue, 9 Mar 2021 08:31:10 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     linux-nvdimm@...ts.01.org, Christoph Hellwig <hch@....de>,
        Ming Lei <ming.lei@...hat.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Hannes Reinecke <hare@...e.de>, Jens Axboe <axboe@...nel.dk>,
        kernel test robot <lkp@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH] libnvdimm: Let revalidate_disk() revalidate region
 read-only

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?