[Devel] [PATCH hci-8.1] dm-ploop: fix a forward notify_merged updating the wrong delta

* [Devel] [PATCH hci-8.1] dm-ploop: fix a forward notify_merged updating the wrong delta
@ 2026-11-04 18:55 Denis V. Lunev
  2026-11-04 18:58 ` no-reply
  2026-11-04 19:14 ` Konstantin Khorenko
  0 siblings, 2 replies; 3+ messages in thread
From: Denis V. Lunev @ 2026-11-04 18:55 UTC (permalink / raw)
  To: andrey.zhadchenko; +Cc: devel

From: Denis V. Lunev <den@openvz.org>

ploop_delta_clusters_merged() rereads the delta that took the clusters,
deltas[level + 1] for a forward merge, and stores its file_size,
file_preallocated_area_start and nr_be after notify_delta_merged(). By
then notify_delta_merged() has moved the deltas above @level one slot
down, so the values land in the delta above the one they belong to,
and that one keeps its sizes from before the merge.

With level == top - 2 the top delta gets the sizes and nr_be of the
delta below it. The sizes drive the preallocation of whichever delta
is on top, and nr_be bounds later merges into a delta, so both deltas
are left with wrong values. The ploop library sends only
notify_merged_backward, so this takes a direct dm message.

Store the values into deltas[level] for a forward merge. A backward
merge changes the delta below @level, which does not move.

Fixes: 6ddad5a4d226 ("dm-ploop: Add ploop target driver")
Reported-by: Konstantin Khorenko <khorenko@virtuozzo.com>
https://virtuozzo.atlassian.net/browse/VSTOR-153426
Feature: dm-ploop: ploop target driver
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 drivers/md/dm-ploop-cmd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/md/dm-ploop-cmd.c b/drivers/md/dm-ploop-cmd.c
index 645c5136e7ba..196cd7da306c 100644
--- a/drivers/md/dm-ploop-cmd.c
+++ b/drivers/md/dm-ploop-cmd.c
@@ -918,6 +918,9 @@ static int ploop_delta_clusters_merged(struct ploop *ploop, u8 level,
 
 	notify_delta_merged(ploop, level, &md_root, forward, nr_be);
 
+	/* notify_delta_merged() moved the deltas above @level one slot down */
+	if (forward)
+		changed_level = level;
 	deltas[changed_level].file_size = file_size;
 	deltas[changed_level].file_preallocated_area_start = file_size;
 	deltas[changed_level].nr_be = nr_be;

base-commit: 95ab11e2c57e8468412ca586d4be8cd75b6bfbf0
-- 
2.53.0

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