[PATCH 6.18 045/641] md/raid5: fix IO hang with degraded array with llbitmap

Greg Kroah-Hartman
2026-02-25T01:43:16Z

6.18-stable review patch. If anyone has any objections, please let me know.

------------------

From: Yu Kuai <yukuai@fnnas.com>

[ Upstream commit cd1635d844d26471c56c0a432abdee12fc9ad735 ]

When llbitmap bit state is still unwritten, any new write should force
rcw, as bitmap_ops->blocks_synced() is checked in handle_stripe_dirtying().
However, later the same check is missing in need_this_block(), causing
stripe to deadloop during handling because handle_stripe() will decide
to go to handle_stripe_fill(), meanwhile need_this_block() always return
0 and nothing is handled.

Link: https://lore.kernel.org/linux-raid/20260123182623.3718551-2-yukuai@fnnas.com
Fixes: 5ab829f1971d ("md/md-llbitmap: introduce new lockless bitmap")
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Li Nan <linan122@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/md/raid5.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 1041788a54c20..3b711a1198adb 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3751,9 +3751,14 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s,
struct r5dev *dev = &sh->dev[disk_idx];
struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],
&sh->dev[s->failed_num[1]] };
+ struct mddev *mddev = sh->raid_conf->mddev;
+ bool force_rcw = false;
int i;
- bool force_rcw = (sh->raid_conf->rmw_level == PARITY_DISABLE_RMW);

+ if (sh->raid_conf->rmw_level == PARITY_DISABLE_RMW ||
+ (mddev->bitmap_ops && mddev->bitmap_ops->blocks_synced &&
+ !mddev->bitmap_ops->blocks_synced(mddev, sh->sector)))
+ force_rcw = true;

if (test_bit(R5_LOCKED, &dev->flags) ||
test_bit(R5_UPTODATE, &dev->flags))
--
2.51.0