dm: fix bio splitting and its bio completion order for regular IO (ee1dfad5) · Commits · 戴 / test

dm_queue_split() is removed because __split_and_process_bio() _must_ handle splitting bios to ensure proper bio submission and completion ordering as a bio is split. Otherwise, multiple recursive calls to ->submit_bio will cause multiple split bios to be allocated from the same ->bio_split mempool at the same time. This would result in deadlock in low memory conditions because no progress could be made (only one bio is available in ->bio_split mempool). This fix has been verified to still fix the loss of performance, due to excess splitting, that commit provided. Fixes: ("Revert "dm: always call blk_queue_split() in dm_process_bio()"") Cc: stable@vger.kernel.org # 5.0+, requires custom backport due to 5.9 changes Reported-by:

Ming Lei <ming.lei@redhat.com> Signed-off-by:

Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

+2 −21

Original line number	Diff line number	Diff line
		@@ -1724,23 +1724,6 @@ out:
		return ret;
		}

		static void dm_queue_split(struct mapped_device md, struct dm_target ti, struct bio **bio)
		{
		unsigned len, sector_count;

		sector_count = bio_sectors(*bio);
		len = min_t(sector_t, max_io_len((*bio)->bi_iter.bi_sector, ti), sector_count);

		if (sector_count > len) {
		struct bio split = bio_split(bio, len, GFP_NOIO, &md->queue->bio_split);

		bio_chain(split, *bio);
		trace_block_split(md->queue, split, (*bio)->bi_iter.bi_sector);
		submit_bio_noacct(*bio);
		*bio = split;
		}
		}

		static blk_qc_t dm_process_bio(struct mapped_device *md,
		struct dm_table map, struct bio bio)
		{
		@@ -1768,13 +1751,11 @@ static blk_qc_t dm_process_bio(struct mapped_device *md,
		if (current->bio_list) {
		if (is_abnormal_io(bio))
		blk_queue_split(&bio);
		else
		dm_queue_split(md, ti, &bio);
		/* regular IO is split by __split_and_process_bio */
		}

		if (dm_get_md_type(md) == DM_TYPE_NVME_BIO_BASED)
		return __process_bio(md, map, bio, ti);
		else
		return __split_and_process_bio(md, map, bio);
		}

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