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SubjectRe: [dm-devel] Barriers still not passing on simple dm devices...
On Tue, Mar 24 2009, Mikulas Patocka wrote:
>
>
> On Mon, 23 Mar 2009, Eric Sandeen wrote:
>
> > I've noticed that on 2.6.29-rcX, with Andi's patch
> > (ab4c1424882be9cd70b89abf2b484add355712fa, dm: support barriers on
> > simple devices) barriers are still getting rejected on these simple devices.
> >
> > The problem is in __generic_make_request():
> >
> > if (bio_barrier(bio) && bio_has_data(bio) &&
> > (q->next_ordered == QUEUE_ORDERED_NONE)) {
> > err = -EOPNOTSUPP;
> > goto end_io;
> > }
> >
> > and dm isn't flagging its queue as supporting ordered writes, so it's
> > rejected here.
> >
> > Doing something like this:
> >
> > + if (t->barriers_supported)
> > + blk_queue_ordered(q, QUEUE_ORDERED_DRAIN, NULL);
> >
> > somewhere in dm (I stuck it in dm_table_set_restrictions() - almost
> > certainly the wrong thing to do) did get my dm-linear device to mount
> > with xfs, w/o xfs complaining that its mount-time barrier tests failed.
> >
> > So what's the right way around this? What should dm (or md for that
> > matter) advertise on their queues about ordered-ness? Should there be
> > some sort of "QUEUE_ORDERED_PASSTHROUGH" or something to say "this level
> > doesn't care, ask the next level" or somesuch? Or should it inherit the
> > flag from the next level down? Ideas?
> >
> > Thanks,
> > -Eric
> >
> > --
> > dm-devel mailing list
> > dm-devel@redhat.com
> > https://www.redhat.com/mailman/listinfo/dm-devel
>
> Hi
>
> This is misdesign in generic bio layer and it should be fixed there. I
> think it is blocking barrier support in md-raid1 too. Jens, pls apply the
> attached patch.
>
> Mikulas
>
> ----
>
> Move test for not-supported barriers to __make_request.
>
> This test prevents barriers from being dispatched to device mapper
> and md.
>
> This test is sensible only for drivers that use requests (such as disk
> drivers), not for drivers that use bios.
>
> It is better to fix it in generic code than to make workaround for it
> in device mapper and md.

So you audited any ->make_request_fn style driver and made sure they
rejected barriers?

>
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
>
> ---
> block/blk-core.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> Index: linux-2.6.29-rc6-devel/block/blk-core.c
> ===================================================================
> --- linux-2.6.29-rc6-devel.orig/block/blk-core.c 2009-02-23 18:43:37.000000000 +0100
> +++ linux-2.6.29-rc6-devel/block/blk-core.c 2009-02-23 18:44:27.000000000 +0100
> @@ -1145,6 +1145,12 @@ static int __make_request(struct request
> const int unplug = bio_unplug(bio);
> int rw_flags;
>
> + if (bio_barrier(bio) && bio_has_data(bio) &&
> + (q->next_ordered == QUEUE_ORDERED_NONE)) {
> + bio_endio(bio, -EOPNOTSUPP);
> + return 0;
> + }
> +
> nr_sectors = bio_sectors(bio);
>
> /*
> @@ -1450,11 +1456,6 @@ static inline void __generic_make_reques
> err = -EOPNOTSUPP;
> goto end_io;
> }
> - if (bio_barrier(bio) && bio_has_data(bio) &&
> - (q->next_ordered == QUEUE_ORDERED_NONE)) {
> - err = -EOPNOTSUPP;
> - goto end_io;
> - }
>
> ret = q->make_request_fn(q, bio);
> } while (ret);
> >

--
Jens Axboe



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