From: Li Nan <linan122@xxxxxxxxxx>
When a flush is issued to an RAID array, a child flush IO is created and
issued for each member disk in the RAID array. Since commit b75197e86e6d
("md: Remove flush handling"), each child flush IO has been chained with
the original bio. As a result, the failure of any child IO could modify
the bi_status of the original bio, potentially impacting the upper-layer
filesystem.
Fix the issue by preventing child flush IO from altering the original
bio->bi_status as before. However, this design introduces a known
issue: in the event of a power failure, if a flush IO on a member
disk fails, the upper layers may not be informed. This issue is not easy
to fix and will not be addressed for the time being in this issue.
Fixes: b75197e86e6d ("md: Remove flush handling")
Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
---
drivers/md/md.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 179ee4afe937..67108c397c5a 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -546,6 +546,26 @@ static int mddev_set_closing_and_sync_blockdev(struct mddev *mddev, int opener_n
return 0;
}
+/*
+ * The only difference from bio_chain_endio() is that the current
+ * bi_status of bio does not affect the bi_status of parent.
+ */
+static void md_end_flush(struct bio *bio)
+{
+ struct bio *parent = bio->bi_private;
+
+ /*
+ * If any flush io error before the power failure,
+ * disk data may be lost.
+ */
+ if (bio->bi_status)
+ pr_err("md: %pg flush io error %d\n", bio->bi_bdev,
+ blk_status_to_errno(bio->bi_status));
+
+ bio_put(bio);
+ bio_endio(parent);
+}
+
bool md_flush_request(struct mddev *mddev, struct bio *bio)
{
struct md_rdev *rdev;
@@ -565,7 +585,9 @@ bool md_flush_request(struct mddev *mddev, struct bio *bio)
new = bio_alloc_bioset(rdev->bdev, 0,
REQ_OP_WRITE | REQ_PREFLUSH, GFP_NOIO,
&mddev->bio_set);
- bio_chain(new, bio);
+ new->bi_private = bio;
+ new->bi_end_io = md_end_flush;
+ bio_inc_remaining(bio);
submit_bio(new);
}
--
2.39.2
