On Thu, 31 Aug 2017, NeilBrown wrote: > > The md->bs bioset currently needs the BIOSET_NEED_RESCUER flag > which I hope to deprecate. It is currently needed because > __split_and_process_bio() can potentially allocate from the > bioset multiple times within the one make_request_fn context. > Subsequent allocations can deadlock waiting for the bio returned > by the first allocation to complete - but it is stuck on the > current->bio_list list. > > The bioset is also used in setup_clone() in dm-rq.c, but there a > non-blocking (GFP_ATOMIC) allocation is used, so there is no risk of > deadlock. > > dm also provide rescuing for ->map() calls. If a map call ever blocks, > any bios already submitted with generic_make_request() will be passed to > the bioset rescuer thread. > > This patch unifies these two separate needs for rescuing bios into a > single mechanism, and use the md->wq work queue to do the rescuing. > > A blk_plug_cb is added to 'struct clone_info' so that it is available > throughout the __split_and_process_bio() process. > Prior to allocating from the bioset, or calling ->map(), > dm_offload_check() is called to ensure that the blk_plug_cb is active. > If either of these operation schedules, the callback is called, > and any queued bios get passed to the wq. > > Note that only current->bio_list[0] is offloaded. current->bio_list[1] > contains bios that were scheduled *before* the current one started, so These bios need to be offloaded too, otherwise you re-introduce this deadlock: https://www.redhat.com/archives/dm-devel/2014-May/msg00089.html Mikulas > they must have been submitted from higher up the stack, and we cannot be > waiting for them here. Also, we now rescue *all* bios on the list as > there is nothing to be gained by being more selective. > > This allows us to remove BIOSET_NEED_RESCUER when allocating this > bioset. > It also keeps all the mechanics of rescuing inside dm, so dm can > be in full control. > > Signed-off-by: NeilBrown <neilb@xxxxxxxx> > --- > > Hi, > I have only tested this lightly as I don't have any test infrastructure > for dm and don't know how to reproduce the expected deadlocks. > I'm keen to know your thoughts on this approach if you find a few spare > moment to have a look. > > Thanks, > NeilBrown > > > drivers/md/dm-core.h | 1 + > drivers/md/dm.c | 99 ++++++++++++++++++++++++++-------------------------- > 2 files changed, 51 insertions(+), 49 deletions(-) > > diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h > index 24eddbdf2ab4..cb060dd6d3ca 100644 > --- a/drivers/md/dm-core.h > +++ b/drivers/md/dm-core.h > @@ -71,6 +71,7 @@ struct mapped_device { > struct work_struct work; > spinlock_t deferred_lock; > struct bio_list deferred; > + struct bio_list rescued; > > /* > * Event handling. > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > index 2edbcc2d7d3f..774dd71cb49a 100644 > --- a/drivers/md/dm.c > +++ b/drivers/md/dm.c > @@ -1134,65 +1134,63 @@ void dm_remap_zone_report(struct dm_target *ti, struct bio *bio, sector_t start) > } > EXPORT_SYMBOL_GPL(dm_remap_zone_report); > > +struct clone_info { > + struct mapped_device *md; > + struct dm_table *map; > + struct bio *bio; > + struct dm_io *io; > + sector_t sector; > + unsigned sector_count; > + struct blk_plug plug; > + struct blk_plug_cb cb; > +}; > + > /* > * Flush current->bio_list when the target map method blocks. > * This fixes deadlocks in snapshot and possibly in other targets. > */ > -struct dm_offload { > - struct blk_plug plug; > - struct blk_plug_cb cb; > -}; > > static void flush_current_bio_list(struct blk_plug_cb *cb, bool from_schedule) > { > - struct dm_offload *o = container_of(cb, struct dm_offload, cb); > + struct clone_info *ci = container_of(cb, struct clone_info, cb); > struct bio_list list; > - struct bio *bio; > - int i; > > - INIT_LIST_HEAD(&o->cb.list); > + INIT_LIST_HEAD(&cb->list); > > - if (unlikely(!current->bio_list)) > + if (unlikely(!current->bio_list || bio_list_empty(¤t->bio_list[0]))) > return; > > - for (i = 0; i < 2; i++) { > - list = current->bio_list[i]; > - bio_list_init(¤t->bio_list[i]); > - > - while ((bio = bio_list_pop(&list))) { > - struct bio_set *bs = bio->bi_pool; > - if (unlikely(!bs) || bs == fs_bio_set || > - !bs->rescue_workqueue) { > - bio_list_add(¤t->bio_list[i], bio); > - continue; > - } > + list = current->bio_list[0]; > + bio_list_init(¤t->bio_list[0]); > + spin_lock(&ci->md->deferred_lock); > + bio_list_merge(&ci->md->rescued, &list); > + spin_unlock(&ci->md->deferred_lock); > + queue_work(ci->md->wq, &ci->md->work); > +} > > - spin_lock(&bs->rescue_lock); > - bio_list_add(&bs->rescue_list, bio); > - queue_work(bs->rescue_workqueue, &bs->rescue_work); > - spin_unlock(&bs->rescue_lock); > - } > - } > +static void dm_offload_start(struct clone_info *ci) > +{ > + blk_start_plug(&ci->plug); > + INIT_LIST_HEAD(&ci->cb.list); > + ci->cb.callback = flush_current_bio_list; > } > > -static void dm_offload_start(struct dm_offload *o) > +static void dm_offload_end(struct clone_info *ci) > { > - blk_start_plug(&o->plug); > - o->cb.callback = flush_current_bio_list; > - list_add(&o->cb.list, ¤t->plug->cb_list); > + list_del(&ci->cb.list); > + blk_finish_plug(&ci->plug); > } > > -static void dm_offload_end(struct dm_offload *o) > +static void dm_offload_check(struct clone_info *ci) > { > - list_del(&o->cb.list); > - blk_finish_plug(&o->plug); > + if (list_empty(&ci->cb.list)) > + list_add(&ci->cb.list, ¤t->plug->cb_list); > } > > -static void __map_bio(struct dm_target_io *tio) > +static void __map_bio(struct clone_info *ci, struct dm_target_io *tio) > { > int r; > sector_t sector; > - struct dm_offload o; > struct bio *clone = &tio->clone; > struct dm_target *ti = tio->ti; > > @@ -1206,9 +1204,8 @@ static void __map_bio(struct dm_target_io *tio) > atomic_inc(&tio->io->io_count); > sector = clone->bi_iter.bi_sector; > > - dm_offload_start(&o); > + dm_offload_check(ci); > r = ti->type->map(ti, clone); > - dm_offload_end(&o); > > switch (r) { > case DM_MAPIO_SUBMITTED: > @@ -1233,15 +1230,6 @@ static void __map_bio(struct dm_target_io *tio) > } > } > > -struct clone_info { > - struct mapped_device *md; > - struct dm_table *map; > - struct bio *bio; > - struct dm_io *io; > - sector_t sector; > - unsigned sector_count; > -}; > - > static void bio_setup_sector(struct bio *bio, sector_t sector, unsigned len) > { > bio->bi_iter.bi_sector = sector; > @@ -1291,6 +1279,7 @@ static struct dm_target_io *alloc_tio(struct clone_info *ci, > struct dm_target_io *tio; > struct bio *clone; > > + dm_offload_check(ci); > clone = bio_alloc_bioset(GFP_NOIO, 0, ci->md->bs); > tio = container_of(clone, struct dm_target_io, clone); > > @@ -1314,7 +1303,7 @@ static void __clone_and_map_simple_bio(struct clone_info *ci, > if (len) > bio_setup_sector(clone, ci->sector, *len); > > - __map_bio(tio); > + __map_bio(ci, tio); > } > > static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti, > @@ -1361,7 +1350,7 @@ static int __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti, > free_tio(tio); > break; > } > - __map_bio(tio); > + __map_bio(ci, tio); > } > > return r; > @@ -1493,6 +1482,7 @@ static void __split_and_process_bio(struct mapped_device *md, > bio_io_error(bio); > return; > } > + dm_offload_start(&ci); > > ci.map = map; > ci.md = md; > @@ -1521,6 +1511,7 @@ static void __split_and_process_bio(struct mapped_device *md, > while (ci.sector_count && !error) > error = __split_and_process_non_flush(&ci); > } > + dm_offload_end(&ci); > > /* drop the extra reference count */ > dec_pending(ci.io, error); > @@ -2248,6 +2239,16 @@ static void dm_wq_work(struct work_struct *work) > int srcu_idx; > struct dm_table *map; > > + if (!bio_list_empty(&md->rescued)) { > + struct bio_list list; > + spin_lock_irq(&md->deferred_lock); > + list = md->deferred; > + bio_list_init(&md->deferred); > + spin_unlock_irq(&md->deferred_lock); > + while ((c = bio_list_pop(&md->deferred)) != NULL) > + generic_make_request(c); > + } > + > map = dm_get_live_table(md, &srcu_idx); > > while (!test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) { > @@ -2796,7 +2797,7 @@ struct dm_md_mempools *dm_alloc_md_mempools(struct mapped_device *md, enum dm_qu > BUG(); > } > > - pools->bs = bioset_create(pool_size, front_pad, BIOSET_NEED_RESCUER); > + pools->bs = bioset_create(pool_size, front_pad, 0); > if (!pools->bs) > goto out; > > -- > 2.14.0.rc0.dirty > > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
