On Tue, Dec 04, 2018 at 03:28:07PM -0500, Mike Snitzer wrote: > On Tue, Dec 04 2018 at 1:35pm -0500, > Dennis Zhou <[email protected]> wrote: > > > The next patch changes the macro bio_set_dev() to associate a bio with a > > blkg based on the device set. However, dm creates a static bio to be > > used as the basis for cloning empty flush bios on creation. The > > bio_set_dev() call in alloc_dev() will cause problems with the next > > patch adding association to bio_set_dev() because the call is before the > > bdev is associated with a gendisk (bd_disk is %NULL). To get around > > this, set the device on the static bio every time and use that to clone > > to the other bios. > > > > Signed-off-by: Dennis Zhou <[email protected]> > > Cc: Alasdair Kergon <[email protected]> > > Cc: Mike Snitzer <[email protected]> > > --- > > block/bio.c | 1 + > > drivers/md/dm.c | 12 +++++++++++- > > 2 files changed, 12 insertions(+), 1 deletion(-) > > > > diff --git a/block/bio.c b/block/bio.c > > index 452b8e79b998..41ebb3f8e2fc 100644 > > --- a/block/bio.c > > +++ b/block/bio.c > > @@ -2021,6 +2021,7 @@ void bio_disassociate_blkg(struct bio *bio) > > bio->bi_blkg = NULL; > > } > > } > > +EXPORT_SYMBOL_GPL(bio_disassociate_blkg); > > > > /** > > * __bio_associate_blkg - associate a bio with the a blkg > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > > index a733e4c920af..a2d6f8b33d23 100644 > > --- a/drivers/md/dm.c > > +++ b/drivers/md/dm.c > > @@ -1417,10 +1417,21 @@ static int __send_empty_flush(struct clone_info *ci) > > unsigned target_nr = 0; > > struct dm_target *ti; > > > > + /* > > + * Empty flush uses a statically initialized bio as the base for > > + * cloning, &md->flush_bio. However, blkg association requires that > > Would prefer: > "Empty flush uses a statically initialized bio, &md->flush_bio, as the > base for cloning. ..." >
Cool, that reads better. > > + * a bdev is associated with a gendisk, which doesn't happen until the > > + * bdev is opened. So, blkg association is done at issue time of the > > + * flush rather than when the device is created in dm_alloc(). > > Another nit but I think you mean "alloc_dev()" here .......^ > Yeah, I did mean alloc_dev(). Fixed. > > + */ > > + bio_set_dev(ci->bio, ci->io->md->bdev); > > + > > BUG_ON(bio_has_data(ci->bio)); > > while ((ti = dm_table_get_target(ci->map, target_nr++))) > > __send_duplicate_bios(ci, ti, ti->num_flush_bios, NULL); > > > > + bio_disassociate_blkg(ci->bio); > > + > > return 0; > > } > > > > @@ -1939,7 +1950,6 @@ static struct mapped_device *alloc_dev(int minor) > > goto bad; > > > > bio_init(&md->flush_bio, NULL, 0); > > - bio_set_dev(&md->flush_bio, md->bdev); > > md->flush_bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC; > > > > dm_stats_init(&md->stats); > > The top-level DM device's bdev->bd_disk is only assigned after the first > blkdev_get(), so I can see why this is needed. > > Think this type of life-cycle quirk was the kind of thing that caused > blk cgroup issues with DM. > > Left wondering whether there would be a better way of handling N flush > bios for DM devices. But for the now this will have to do. > > Acked-by: Mike Snitzer <[email protected]> > Thanks, Dennis
