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FAILED: patch "[PATCH] dm: fix bio splitting and its bio completion order for" failed to apply to 5.8-stable tree

PATCH [email protected] 1 participant 1 message Sep 28, 2020

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The patch below does not apply to the 5.8-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ee1dfad5325ff1cfb2239e564cd411b3bfe8667a Mon Sep 17 00:00:00 2001
From: Mike Snitzer <[email protected]>
Date: Mon, 14 Sep 2020 13:04:19 -0400
Subject: [PATCH] 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 commit 120c9257f5f1 provided.

Fixes 120c9257f5f1 ("Revert "dm: always call blk_queue_split() in dm_process_bio()"")
Cc [email protected] # 5.0+, requires custom backport due to 5.9 changes
Reported-by Ming Lei <[email protected]>
Signed-off-by Mike Snitzer <[email protected]>
drivers/md/dm.c +2 -21
index 4a40df8af7d3..d948cd522431 100644
@@ -1724,23 +1724,6 @@ static blk_qc_t __process_bio(struct mapped_device *md, struct dm_table *map,
 	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)
 {

@@ -1768,14 +1751,12 @@ 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);
+	return __split_and_process_bio(md, map, bio);
 }
 
 static blk_qc_t dm_submit_bio(struct bio *bio)