[Devel] [PATCH hci-8.1 v11 05/10] dm-qcow2: flush lower md before clearing dirty bit on merge failure

[Alexander Ivanov <alexander.ivanov@virtuozzo.com>]

When qcow2_merge_common() fails, qcow2_merge_backward_work() clears the
dirty bit of the lower image right away. qcow2_service_iter() waits only
for the service qios, so delayed md writeback of the lower image may
still be pending. With kernel_sets_dirty_bit, a crash at that point
leaves the lower image marked clean on disk with refblocks that lag
behind the merged data.

Flush the deferred activity of the lower image before writing its
header, as qcow2_merge_backward_complete() does.

https://virtuozzo.atlassian.net/browse/VSTOR-148171
Feature: dm-qcow2: block device over QCOW2 files driver
Fixes: 222b6f1291c1c ("dm-qcow2: Introduce driver to create block devices over QCOW2 files")

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
---
 drivers/md/dm-qcow2-cmd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/dm-qcow2-cmd.c b/drivers/md/dm-qcow2-cmd.c
index 45c517ce0ef8..3bccce090f01 100644
--- a/drivers/md/dm-qcow2-cmd.c
+++ b/drivers/md/dm-qcow2-cmd.c
@@ -330,6 +330,7 @@ void qcow2_merge_backward_work(struct work_struct *work)
 	ret = qcow2_merge_common(tgt, qcow2);
 	if (ret) {
 		set_backward_merge_in_process(tgt, qcow2, false);
+		qcow2_flush_deferred_activity(tgt, lower);
 		ret2 = qcow2_set_image_file_features(lower, false);
 		if (ret2 < 0)
 			QC_ERR(tgt->ti, "Can't unuse lower (%d)", ret2);
-- 
2.53.0

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