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SubjectRe: [PATCH] dm writecache: reject asynchronous pmem.
On Tue, Jun 30, 2020 at 09:32:01AM -0400, Mikulas Patocka wrote:
>
>
> 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?
That should be always the case at this point.
>
> 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.
This is to prevent the situation where we have WC_MODE_PMEM(wc) but
cannot guarantee consistency because the async flush is not handled.

Thanks

Michal

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