[PATCH] btrfs: zoned: skip fully truncated ordered extents at zone finish

A fully truncated ordered extent (truncated_len == 0) wrote no data, so its
->csum_list is empty and btrfs_finish_ordered_zoned() trips:

  assertion failed: !list_empty(&ordered->csum_list), in fs/btrfs/zoned.c:2141

Since commit 66ff4d366e7e a short or cancelled direct IO write finishes the
unsubmitted ordered extent as truncated with uptodate = true instead of
setting BTRFS_ORDERED_IOERR, so it now reaches btrfs_finish_ordered_zoned()
rather than being skipped by the IOERR check in btrfs_finish_ordered_io().
generic/208 hits this on a zoned filesystem.

Return early for these, like the BTRFS_ORDERED_PREALLOC case; there is no
zone append result to record and btrfs_finish_one_ordered() skips them too.

Fixes: 66ff4d366e7e ("btrfs: fix false IO failure after falling back to buffered write")
Signed-off-by: Johannes Thumshirn <[email protected]>
---
 fs/btrfs/zoned.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index bff209b552c3..9668a5928735 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -2138,6 +2138,16 @@ void btrfs_finish_ordered_zoned(struct btrfs_ordered_extent *ordered)
 	if (test_bit(BTRFS_ORDERED_PREALLOC, &ordered->flags))
 		return;
 
+	/*
+	 * A fully truncated ordered extent wrote no data and so has
+	 * no zone append result to record.
+	 */
+	if (test_bit(BTRFS_ORDERED_TRUNCATED, &ordered->flags) &&
+	    ordered->truncated_len == 0) {
+		ASSERT(list_empty(&ordered->csum_list));
+		return;
+	}
+
 	ASSERT(!list_empty(&ordered->csum_list));
 	sum = list_first_entry(&ordered->csum_list, struct btrfs_ordered_sum, list);
 	logical = sum->logical;
-- 
2.54.0