Hi This is backport of upstream commit d67a5f4b5947aba4bfe9a80a2b86079c215ca755. It is suitable for stable branches 3.10 and 3.12.
Mikulas commit d67a5f4b5947aba4bfe9a80a2b86079c215ca755 Author: Mikulas Patocka <[email protected]> Date: Wed Feb 15 11:26:10 2017 -0500 dm: flush queued bios when process blocks to avoid deadlock Commit df2cb6daa4 ("block: Avoid deadlocks with bio allocation by stacking drivers") created a workqueue for every bio set and code in bio_alloc_bioset() that tries to resolve some low-memory deadlocks by redirecting bios queued on current->bio_list to the workqueue if the system is low on memory. However other deadlocks (see below **) may happen, without any low memory condition, because generic_make_request is queuing bios to current->bio_list (rather than submitting them). ** the related dm-snapshot deadlock is detailed here: https://www.redhat.com/archives/dm-devel/2016-July/msg00065.html Fix this deadlock by redirecting any bios on current->bio_list to the bio_set's rescue workqueue on every schedule() call. Consequently, when the process blocks on a mutex, the bios queued on current->bio_list are dispatched to independent workqueus and they can complete without waiting for the mutex to be available. The structure blk_plug contains an entry cb_list and this list can contain arbitrary callback functions that are called when the process blocks. To implement this fix DM (ab)uses the onstack plug's cb_list interface to get its flush_current_bio_list() called at schedule() time. This fixes the snapshot deadlock - if the map method blocks, flush_current_bio_list() will be called and it redirects bios waiting on current->bio_list to appropriate workqueues. Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1267650 Depends-on: df2cb6daa4 ("block: Avoid deadlocks with bio allocation by stacking drivers") Signed-off-by: Mikulas Patocka <[email protected]> Signed-off-by: Mike Snitzer <[email protected]> --- drivers/md/dm.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) Index: linux-stable/drivers/md/dm.c =================================================================== --- linux-stable.orig/drivers/md/dm.c +++ linux-stable/drivers/md/dm.c @@ -1075,11 +1075,62 @@ int dm_set_target_max_io_len(struct dm_t } EXPORT_SYMBOL_GPL(dm_set_target_max_io_len); +/* + * 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 bio_list list; + struct bio *bio; + + INIT_LIST_HEAD(&o->cb.list); + + if (unlikely(!current->bio_list)) + return; + + list = *current->bio_list; + bio_list_init(current->bio_list); + + while ((bio = bio_list_pop(&list))) { + struct bio_set *bs = bio->bi_pool; + if (unlikely(!bs) || bs == fs_bio_set) { + bio_list_add(current->bio_list, bio); + continue; + } + + 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 dm_offload *o) +{ + blk_start_plug(&o->plug); + o->cb.callback = flush_current_bio_list; + list_add(&o->cb.list, ¤t->plug->cb_list); +} + +static void dm_offload_end(struct dm_offload *o) +{ + list_del(&o->cb.list); + blk_finish_plug(&o->plug); +} + static void __map_bio(struct dm_target_io *tio) { int r; sector_t sector; struct mapped_device *md; + struct dm_offload o; struct bio *clone = &tio->clone; struct dm_target *ti = tio->ti; @@ -1093,7 +1144,11 @@ static void __map_bio(struct dm_target_i */ atomic_inc(&tio->io->io_count); sector = clone->bi_sector; + + dm_offload_start(&o); r = ti->type->map(ti, clone); + dm_offload_end(&o); + if (r == DM_MAPIO_REMAPPED) { /* the bio has been remapped so dispatch it */ -- dm-devel mailing list [email protected] https://www.redhat.com/mailman/listinfo/dm-devel
