dm: fix bio splitting and its bio completion order for regular IO
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 commit120c9257f5
provided. Fixes:120c9257f5
("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>
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@ -1724,23 +1724,6 @@ out:
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return ret;
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}
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static void dm_queue_split(struct mapped_device *md, struct dm_target *ti, struct bio **bio)
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{
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unsigned len, sector_count;
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sector_count = bio_sectors(*bio);
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len = min_t(sector_t, max_io_len((*bio)->bi_iter.bi_sector, ti), sector_count);
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if (sector_count > len) {
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struct bio *split = bio_split(*bio, len, GFP_NOIO, &md->queue->bio_split);
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bio_chain(split, *bio);
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trace_block_split(md->queue, split, (*bio)->bi_iter.bi_sector);
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submit_bio_noacct(*bio);
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*bio = split;
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}
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}
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static blk_qc_t dm_process_bio(struct mapped_device *md,
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struct dm_table *map, struct bio *bio)
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{
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@ -1768,13 +1751,11 @@ static blk_qc_t dm_process_bio(struct mapped_device *md,
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if (current->bio_list) {
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if (is_abnormal_io(bio))
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blk_queue_split(&bio);
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else
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dm_queue_split(md, ti, &bio);
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/* regular IO is split by __split_and_process_bio */
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}
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if (dm_get_md_type(md) == DM_TYPE_NVME_BIO_BASED)
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return __process_bio(md, map, bio, ti);
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else
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return __split_and_process_bio(md, map, bio);
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}
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