[PATCH 4/4] md/raid10: reset read_slot when reusing r10bio for discard

["Chen Cheng" <chencheng@fnnas.com>]

From: Chen Cheng <chencheng@fnnas.com>

raid10_handle_discard() reuses r10bio objects from r10bio_pool.

put_all_bios() always drops devs[i].bio, but it only drops
devs[i].repl_bio when r10_bio->read_slot < 0. If discard reuses an
r10bio that was previously used for a read, read_slot can still be
non-negative, and discard cleanup can skip bio_put() on repl_bio.

Reset read_slot to -1 when preparing an r10bio for discard so the
replacement bio is always released correctly.
---
 drivers/md/raid10.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 3edde440623a..19d7f6f62beb 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1764,6 +1764,7 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
 	r10_bio->mddev = mddev;
 	r10_bio->state = 0;
 	r10_bio->sectors = 0;
+	r10_bio->read_slot = -1;
 	r10_bio->used_nr_devs = geo->raid_disks;
 	memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * geo->raid_disks);
 	wait_blocked_dev(mddev, r10_bio);
-- 
2.53.0