[PATCH v4 3/5] iomap: fix incorrect did_zero setting in iomap_zero_iter()

From: Zhang Yi <[email protected]>

The did_zero output parameter was unconditionally set after the loop,
which is incorrect. It should only be set when the zeroing operation
actually completes, not when IOMAP_F_STALE is set or when
IOMAP_F_FOLIO_BATCH is set but !folio causes the loop to break early,
or when iomap_iter_advance() returns an error.

This causes did_zero to be incorrectly set when zeroing a clean
unwritten extent because the loop exits early without actually zeroing
any data.

Fix it by using a local variable to track whether any folio was actually
zeroed, and only set did_zero after the loop if zeroing happened.

Fixes: 98eb8d95025b ("iomap: set did_zero to true when zeroing successfully")
Signed-off-by: Zhang Yi <[email protected]>
Reviewed-by: "Darrick J. Wong" <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
---
 fs/iomap/buffered-io.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index aeeed6316cf9..7f77a1f68160 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1542,6 +1542,7 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
 		const struct iomap_write_ops *write_ops)
 {
 	u64 bytes = iomap_length(iter);
+	bool zeroed = false;
 	int status;
 
 	do {
@@ -1560,6 +1561,8 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
 		/* a NULL folio means we're done with a folio batch */
 		if (!folio) {
 			status = iomap_iter_advance_full(iter);
+			if (status)
+				return status;
 			break;
 		}
 
@@ -1570,6 +1573,7 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
 				bytes);
 
 		folio_zero_range(folio, offset, bytes);
+		zeroed = true;
 		folio_mark_accessed(folio);
 
 		ret = iomap_write_end(iter, bytes, bytes, folio);
@@ -1579,10 +1583,10 @@ static int iomap_zero_iter(struct iomap_iter *iter, bool *did_zero,
 
 		status = iomap_iter_advance(iter, bytes);
 		if (status)
-			break;
+			return status;
 	} while ((bytes = iomap_length(iter)) > 0);
 
-	if (did_zero)
+	if (did_zero && zeroed)
 		*did_zero = true;
 	return status;
 }
-- 
2.52.0