linux-kernel - [PATCH v8 4/4] fix origin_map - don't split a bio for the origin device if it does not have registered snapshots.

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Date:   Fri, 9 Apr 2021 14:48:04 +0300
From:   Sergei Shtepa <sergei.shtepa@...am.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Hannes Reinecke <hare@...e.de>,
        Mike Snitzer <snitzer@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, <dm-devel@...hat.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <sergei.shtepa@...am.com>, <pavel.tide@...am.com>
Subject: [PATCH v8 4/4] fix origin_map - don't split a bio for the origin device if it does not have registered snapshots.

Signed-off-by: Sergei Shtepa <sergei.shtepa@...am.com>
---
 drivers/md/dm-snap.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 11890db71f3f..81e8e3bb6d25 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -2685,11 +2685,18 @@ static int origin_map(struct dm_target *ti, struct bio *bio)
 	if (bio_data_dir(bio) != WRITE)
 		return DM_MAPIO_REMAPPED;
 
-	available_sectors = o->split_boundary -
-		((unsigned)bio->bi_iter.bi_sector & (o->split_boundary - 1));
+	/*
+	 * If no snapshot is connected to origin, then split_boundary
+	 * will be set to zero. In this case, we don't need to split a bio.
+	 */
+	if (o->split_boundary) {
+		available_sectors = o->split_boundary -
+			((unsigned int)bio->bi_iter.bi_sector &
+				(o->split_boundary - 1));
 
-	if (bio_sectors(bio) > available_sectors)
-		dm_accept_partial_bio(bio, available_sectors);
+		if (bio_sectors(bio) > available_sectors)
+			dm_accept_partial_bio(bio, available_sectors);
+	}
 
 	/* Only tell snapshots if this is a write */
 	return do_origin(o->dev, bio, true);
-- 
2.20.1