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

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Date:   Wed, 10 Mar 2021 09:33:52 +0000
From:   "Verma, Vishal L" <vishal.l.verma@...el.com>
To:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
CC:     lkp <lkp@...el.com>, "hch@....de" <hch@....de>,
        "hare@...e.de" <hare@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>
Subject: 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@....de>
> Cc: Ming Lei <ming.lei@...hat.com>
> Cc: Martin K. Petersen <martin.petersen@...cle.com>
> Cc: Hannes Reinecke <hare@...e.de>
> Cc: Jens Axboe <axboe@...nel.dk>
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: Vishal Verma <vishal.l.verma@...el.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
> 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
> 
>  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@...el.com>