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. ..." > + * 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 .......^ > + */ > + 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, Mike
