[PATCH 3/6] iomap: advance the ifs allocation if we have more than one blocks per folio

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

Now we allocate ifs if i_blocks_per_folio is larger than one when
writing back dirty folios in iomap_writepage_map(), so we don't attach
an ifs after buffer write to an entire folio until it starts writing
back, if we partial truncate that folio, iomap_invalidate_folio() can't
clear counterpart block's dirty bit as expected. Fix this by advance the
ifs allocation to __iomap_write_begin().

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/iomap/buffered-io.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 64c4808fab31..ec17bf8d62e9 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -686,6 +686,12 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
 	size_t from = offset_in_folio(folio, pos), to = from + len;
 	size_t poff, plen;
 
+	if (nr_blocks > 1) {
+		ifs = ifs_alloc(iter->inode, folio, iter->flags);
+		if ((iter->flags & IOMAP_NOWAIT) && !ifs)
+			return -EAGAIN;
+	}
+
 	/*
 	 * If the write or zeroing completely overlaps the current folio, then
 	 * entire folio will be dirtied so there is no need for
@@ -697,10 +703,6 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
 	    pos + len >= folio_pos(folio) + folio_size(folio))
 		return 0;
 
-	ifs = ifs_alloc(iter->inode, folio, iter->flags);
-	if ((iter->flags & IOMAP_NOWAIT) && !ifs && nr_blocks > 1)
-		return -EAGAIN;
-
 	if (folio_test_uptodate(folio))
 		return 0;
 	folio_clear_error(folio);
@@ -1913,7 +1915,12 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
 	WARN_ON_ONCE(end_pos <= pos);
 
 	if (i_blocks_per_folio(inode, folio) > 1) {
-		if (!ifs) {
+		/*
+		 * This should not happen since we always allocate ifs in
+		 * iomap_folio_mkwrite_iter() and there is more than one
+		 * blocks per folio in __iomap_write_begin().
+		 */
+		if (WARN_ON_ONCE(!ifs)) {
 			ifs = ifs_alloc(inode, folio, 0);
 			iomap_set_range_dirty(folio, 0, end_pos - pos);
 		}
-- 
2.39.2