diff mbox series

dm writecache: reject asynchronous pmem.

Message ID 20200630123528.29660-1-msuchanek@suse.de (mailing list archive)
State Superseded
Headers show
Series dm writecache: reject asynchronous pmem. | expand

Commit Message

Michal Suchánek June 30, 2020, 12:35 p.m. UTC
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(+)

Comments

Mikulas Patocka June 30, 2020, 1:32 p.m. UTC | #1
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
Mike Snitzer June 30, 2020, 1:36 p.m. UTC | #2
On Tue, Jun 30 2020 at 10:10am -0400,
Michal Suchánek <msuchanek@suse.de> wrote:

> 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.

The writecache operates in 2 modes.  SSD or PMEM.  Mikulas is saying
your dax_synchronous() check should go within a WC_MODE_PMEM(wc) block
because it doesn't make sense to do the check when in SSD mode.

Mike
Michal Suchánek June 30, 2020, 2:10 p.m. UTC | #3
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
Michal Suchánek June 30, 2020, 2:43 p.m. UTC | #4
On Tue, Jun 30, 2020 at 09:36:33AM -0400, Mike Snitzer wrote:
> On Tue, Jun 30 2020 at 10:10am -0400,
> Michal Suchánek <msuchanek@suse.de> wrote:
> 
> > 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.
> 
> The writecache operates in 2 modes.  SSD or PMEM.  Mikulas is saying
> your dax_synchronous() check should go within a WC_MODE_PMEM(wc) block
> because it doesn't make sense to do the check when in SSD mode.

Indeed, it's in the wrong if/else branch.

Thanks

Michal
diff mbox series

Patch

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)) {