[Devel] [PATCH hci-8.1 v9 07/10] dm-qcow2: fix md page cleanup on failed reftable relocation

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

relocate_refcount_table() inserts an md page for every page of the new
reftable tail and of the new refblocks, starting at
pos + old_clus * clu_size, but its error path erases only one page per
cluster starting at end. The remaining pages stay in qcow2->md_pages.
Since a failed relocation leaves the header and reftable_max_file_size
unchanged, the next relocation picks the same pos, gets -EEXIST from
md_page_try_insert() and fails with -EIO. So a single -ENOMEM or header
write error makes every later relocation fail until the target is
reloaded.

Erase every page the allocation loop inserted.

Failures after the in-memory header is switched to the new reftable
also jumped there. At that point the new pages back the live reftable
and may be dirty and linked in slow_wb_batch_list, so freeing them
leaves writeback with freed pages. Just return -EIO on these paths, as
freeing with the fixed range would also free the dirty reftable tail.

https://virtuozzo.atlassian.net/browse/VSTOR-148171
Feature: dm-qcow2: block device over QCOW2 files driver

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
---
 drivers/md/dm-qcow2-map.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
index fa63bd6acfb8..f6e66799bf27 100644
--- a/drivers/md/dm-qcow2-map.c
+++ b/drivers/md/dm-qcow2-map.c
@@ -2372,21 +2372,21 @@ static int relocate_refcount_table(struct qcow2 *qcow2, struct qio **qio)
 		if (!WARN_ON_ONCE(!md))
 			qcow2_md_make_dirty(qcow2, md, true);
 		if (!md)
-			break; /* goto err_free_r2_pages */
+			break;
 	}
 	spin_unlock_irq(&qcow2->md_pages_lock);
 	if (i != nr_pages)
-		goto err_free_r2_pages;
+		return -EIO;
 
 	/* Connect new R2 to new R1 */
 	for (i = end; i < r2_end; i += clu_size) {
 		if (calc_refcounters_map(qcow2, i, &r1, &r2) < 0) {
 			WARN_ON_ONCE(1);
-			goto err_free_r2_pages;
+			return -EIO;
 		}
 		ret = handle_md_page(qcow2, r1.page_id, NULL, &md);
 		if (WARN_ON_ONCE(ret <= 0))
-			goto err_free_r2_pages;
+			return -EIO;
 		spin_lock_irq(&qcow2->md_pages_lock);
 		set_u64_to_be_page(md->page, r1.index_in_page, i);
 		qcow2_md_make_dirty(qcow2, md, true);
@@ -2397,7 +2397,7 @@ static int relocate_refcount_table(struct qcow2 *qcow2, struct qio **qio)
 	for (i = pos; i < r2_end; i += clu_size) {
 		ret = qcow2_handle_r1r2_maps(qcow2, i, NULL, &r1, &r2, false);
 		if (WARN_ON_ONCE(ret <= 0))
-			goto err_free_r2_pages;
+			return -EIO;
 		mark_cluster_used(qcow2, r2.md, r2.index_in_page);
 	}
 
@@ -2405,14 +2405,15 @@ static int relocate_refcount_table(struct qcow2 *qcow2, struct qio **qio)
 	for (i = old_pos; i < old_end; i += clu_size) {
 		ret = qcow2_handle_r1r2_maps(qcow2, i, NULL, &r1, &r2, false);
 		if (WARN_ON_ONCE(ret <= 0))
-			goto err_free_r2_pages;
+			return -EIO;
 		mark_cluster_unused(qcow2, r2.md, r2.index_in_page, i);
 	}
 
 	return 1;
 
 err_free_r2_pages:
-	for (i = end; i < r2_end; i += clu_size) {
+	while (i > pos + (u64)old_clus * clu_size) {
+		i -= PAGE_SIZE;
 		ret = handle_md_page(qcow2, i >> PAGE_SHIFT, NULL, &md);
 		if (ret <= 0)
 			break;
-- 
2.53.0

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