On Tue, Apr 12, 2022 at 08:33:04AM +0900, Damien Le Moal wrote: > On 4/11/22 23:18, Ming Lei wrote: > >>>> This fixes the issue: > >>>> > >>>> diff --git a/drivers/md/dm.c b/drivers/md/dm.c > >>>> index 3c5fad7c4ee6..3dd6735450c5 100644 > >>>> --- a/drivers/md/dm.c > >>>> +++ b/drivers/md/dm.c > >>>> @@ -581,7 +581,7 @@ static struct dm_io *alloc_io(struct mapped_device > >>>> *md, struct bio *bio) > >>>> io->status = 0; > >>>> atomic_set(&io->io_count, 1); > >>>> this_cpu_inc(*md->pending_io); > >>>> - io->orig_bio = NULL; > >>>> + io->orig_bio = bio; > >>>> io->md = md; > >>>> io->map_task = current; > >>>> spin_lock_init(&io->lock); > >>>> > >>>> Otherwise, the dm-zone.c code sees a NULL orig_bio. > >>>> However, this change may be messing up the bio accounting. Need to check that. > >>> > >>> Looks it is one recent regression since: > >>> > >>> commit 0fbb4d93b38b ("dm: add dm_submit_bio_remap interface") > >> > >> Yep, saw that. Problem is, I really do not understand that change setting > >> io->orig_bio *after* __map_bio() is called. It seems that the accounting > >> is done on each fragment of the orig_bio instead of once for the entire > >> BIO... So my "fix" above seems wrong. Apart from passing along orig_bio as > >> an argument to __map_bio() from __split_and_process_bio(), I do not think > >> my change is correct. Thoughts ? > > > > Frankly speaking, both changing ->orig_bio after split and setting ->orig_bio > > after ->map() looks ugly & tricky, and the following change should avoid the > > issue, meantime simplify dm accounting a bit: > > > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > > index 3c5fad7c4ee6..f1fe83113608 100644 > > --- a/drivers/md/dm.c > > +++ b/drivers/md/dm.c > > @@ -581,7 +581,7 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio) > > io->status = 0; > > atomic_set(&io->io_count, 1); > > this_cpu_inc(*md->pending_io); > > - io->orig_bio = NULL; > > + io->orig_bio = bio; > > io->md = md; > > io->map_task = current; > > spin_lock_init(&io->lock); > > @@ -1223,19 +1223,11 @@ void dm_submit_bio_remap(struct bio *clone, struct bio *tgt_clone) > > * Account io->origin_bio to DM dev on behalf of target > > * that took ownership of IO with DM_MAPIO_SUBMITTED. > > */ > > - if (io->map_task == current) { > > + if (io->map_task == current) > > /* Still in target's map function */ > > dm_io_set_flag(io, DM_IO_START_ACCT); > > - } else { > > - /* > > - * Called by another thread, managed by DM target, > > - * wait for dm_split_and_process_bio() to store > > - * io->orig_bio > > - */ > > - while (unlikely(!smp_load_acquire(&io->orig_bio))) > > - msleep(1); > > + else > > Curly brackets around the else here. > > > dm_start_io_acct(io, clone); > > - } > > > > __dm_submit_bio_remap(tgt_clone, disk_devt(io->md->disk), > > tio->old_sector); > > @@ -1562,7 +1554,7 @@ static void dm_split_and_process_bio(struct mapped_device *md, > > struct dm_table *map, struct bio *bio) > > { > > struct clone_info ci; > > - struct bio *orig_bio = NULL; > > + struct bio *new_bio = NULL; > > int error = 0; > > > > init_clone_info(&ci, md, map, bio); > > @@ -1578,22 +1570,14 @@ static void dm_split_and_process_bio(struct mapped_device *md, > > if (error || !ci.sector_count) > > goto out; > > > > - /* > > - * Remainder must be passed to submit_bio_noacct() so it gets handled > > - * *after* bios already submitted have been completely processed. > > - * We take a clone of the original to store in ci.io->orig_bio to be > > - * used by dm_end_io_acct() and for dm_io_complete() to use for > > - * completion handling. > > - */ > > This comment should remain with some adjustment. Fine, just felt the approach is very straightforward. > > > - orig_bio = bio_split(bio, bio_sectors(bio) - ci.sector_count, > > - GFP_NOIO, &md->queue->bio_split); > > - bio_chain(orig_bio, bio); > > - trace_block_split(orig_bio, bio->bi_iter.bi_sector); > > - submit_bio_noacct(bio); > > + new_bio = bio_alloc_clone(bio->bi_bdev, bio, GFP_NOIO, > > + &md->queue->bio_split); > > Why not keep using bio_split() ? With bio_split(), 'bio' actually tracks the remainder, and the returned 'orig_bio' tracks the part for current target io, so ->orig_bio has to be updated in this way. With bio_alloc_clone() and bio_trim(), ->orig_bio needn't to be changed, and assigning it in alloc_io() works perfectly. > > > + bio_trim(new_bio, bio_sectors(bio) - ci.sector_count, ci.sector_count); > > + bio_trim(bio, 0, bio_sectors(bio) - ci.sector_count); > > + bio_chain(new_bio, bio); > > + trace_block_split(new_bio, new_bio->bi_iter.bi_sector); > > + submit_bio_noacct(new_bio); > > out: > > - if (!orig_bio) > > - orig_bio = bio; > > - smp_store_release(&ci.io->orig_bio, orig_bio); > > if (dm_io_flagged(ci.io, DM_IO_START_ACCT)) > > dm_start_io_acct(ci.io, NULL); > > I tested this and it works. Need to check the accounting though. > And I agree this is a lot cleaner :) BTW, the cloned bio for split is just for accounting purpose, if ->bi_iter.bi_sector & ->bi_iter.bi_size can be stored in 'struct dm_io', the cloned bio can be avoided, but code may become not readable as before. Thanks, Ming -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel