The writecache driver does not handle asynchronous pmem. Reject it when
supplied as cache.

Link: https://lore.kernel.org/linux-nvdimm/87lfk5hahc....@linux.ibm.com/
Fixes: 6e84200c0a29 ("virtio-pmem: Add virtio pmem driver")

Signed-off-by: Michal Suchanek <msucha...@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..5358894bb9fd 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -2266,6 +2266,12 @@ static int writecache_ctr(struct dm_target *ti, unsigned 
argc, char **argv)
        }
 
        if (WC_MODE_PMEM(wc)) {
+               if (!dax_synchronous(wc->ssd_dev->dax_dev)) {
+                       r = -EOPNOTSUPP;
+                       ti->error = "Asynchronous persistent memory not 
supported as pmem cache";
+                       goto bad;
+               }
+
                r = persistent_memory_claim(wc);
                if (r) {
                        ti->error = "Unable to map persistent memory for cache";
-- 
2.26.2

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