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Date:   Tue, 30 Jun 2020 09:32:01 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Michal Suchanek <msuchanek@suse.de>
cc:     linux-nvdimm@lists.01.org,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Jan Kara <jack@suse.cz>, Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@redhat.com>, dm-devel@redhat.com,
        Pankaj Gupta <pagupta@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Yuval Shaia <yuval.shaia@oracle.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Jakub Staron <jstaron@google.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] dm writecache: reject asynchronous pmem.
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On Tue, 30 Jun 2020, Michal Suchanek wrote:

> The writecache driver does not handle asynchronous pmem. Reject it when
> supplied as cache.
> 
> Link: https://lore.kernel.org/linux-nvdimm/87lfk5hahc.fsf@linux.ibm.com/
> Fixes: 6e84200c0a29 ("virtio-pmem: Add virtio pmem driver")
> 
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> ---
>  drivers/md/dm-writecache.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
> index 30505d70f423..57b0a972f6fd 100644
> --- a/drivers/md/dm-writecache.c
> +++ b/drivers/md/dm-writecache.c
> @@ -2277,6 +2277,12 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv)
>  
>  		wc->memory_map_size -= (uint64_t)wc->start_sector << SECTOR_SHIFT;
>  
> +		if (!dax_synchronous(wc->ssd_dev->dax_dev)) {
> +			r = -EOPNOTSUPP;
> +			ti->error = "Asynchronous persistent memory not supported as pmem cache";
> +			goto bad;
> +		}
> +
>  		bio_list_init(&wc->flush_list);
>  		wc->flush_thread = kthread_create(writecache_flush_thread, wc, "dm_writecache_flush");
>  		if (IS_ERR(wc->flush_thread)) {
> -- 

Hi

Shouldn't this be in the "if (WC_MODE_PMEM(wc))" block?

WC_MODE_PMEM(wc) retrurns true if we are using persistent memory as a 
cache device, otherwise we are using generic block device as a cache 
device.

Mikulas