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 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 <[email protected]> --- 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
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