This is a note to let you know that I've just added the patch titled dm: fix bio splitting and its bio completion order for regular IO to the 5.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: dm-fix-bio-splitting-and-its-bio-completion-order-for-regular-io.patch and it can be found in the queue-5.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From ee1dfad5325ff1cfb2239e564cd411b3bfe8667a Mon Sep 17 00:00:00 2001 From: Mike Snitzer <snitzer@xxxxxxxxxx> Date: Mon, 14 Sep 2020 13:04:19 -0400 Subject: dm: fix bio splitting and its bio completion order for regular IO From: Mike Snitzer <snitzer@xxxxxxxxxx> commit ee1dfad5325ff1cfb2239e564cd411b3bfe8667a upstream. 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 120c9257f5f1 provided. Fixes: 120c9257f5f1 ("Revert "dm: always call blk_queue_split() in dm_process_bio()"") Cc: stable@xxxxxxxxxxxxxxx # 5.0+, requires custom backport due to 5.9 changes Reported-by: Ming Lei <ming.lei@xxxxxxxxxx> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/md/dm.c | 23 ++--------------------- 1 file changed, 2 insertions(+), 21 deletions(-) --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1728,23 +1728,6 @@ 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); - generic_make_request(*bio); - *bio = split; - } -} - static blk_qc_t dm_process_bio(struct mapped_device *md, struct dm_table *map, struct bio *bio) { @@ -1772,14 +1755,12 @@ static blk_qc_t dm_process_bio(struct ma if (current->bio_list) { if (is_abnormal_io(bio)) blk_queue_split(md->queue, &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); + return __split_and_process_bio(md, map, bio); } static blk_qc_t dm_make_request(struct request_queue *q, struct bio *bio) Patches currently in stable-queue which might be from snitzer@xxxxxxxxxx are queue-5.8/dm-fix-bio-splitting-and-its-bio-completion-order-for-regular-io.patch