[PATCH v2 3/7] exfat: dirty all new pages when extending valid_size

[Chi Zhiling]

From: Chi Zhiling <chizhiling@xxxxxxxxxx>

In the current code, exfat_zero_new_range() does not mark non-uptodate
pages as dirty, which may cause some blocks within a page to not be
written back.

This commit no longer checks each block in a non-uptodate page
individually. Instead, it reads the entire page back into the cache and
then writes it back as a whole. This allows concurrent writes and zeroing
operations to be synchronized using the folio lock.

Signed-off-by: Chi Zhiling <chizhiling@xxxxxxxxxx>
---
 fs/exfat/file.c | 89 ++++++++-----------------------------------------
 1 file changed, 13 insertions(+), 76 deletions(-)

diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index 81eeb76ef94b..e1394c5b016a 100644
--- a/fs/exfat/file.c
+++ b/fs/exfat/file.c
@@ -664,90 +664,27 @@ int exfat_file_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
 static int exfat_zero_new_range(struct inode *inode, loff_t start, loff_t end)
 {
 	struct address_space *mapping = inode->i_mapping;
-	unsigned int blocksize = i_blocksize(inode);
-	loff_t pos = start;
-	int err;
+	loff_t next, pos = start;
+	struct folio *folio;
+	pgoff_t index;
 
 	while (pos < end) {
-		loff_t next = min_t(loff_t,
-				round_down(pos, PAGE_SIZE) + PAGE_SIZE, end);
-		struct folio *folio;
-		loff_t bpos;
-
-		folio = filemap_get_folio(mapping, pos >> PAGE_SHIFT);
-		if (IS_ERR(folio)) {
-			err = iomap_zero_range(inode, pos, next - pos, NULL,
-					       &exfat_iomap_ops, NULL, NULL);
-			if (err < 0)
-				return err;
-			pos = next;
-			continue;
-		}
+		index = pos >> PAGE_SHIFT;
+		next = min_t(loff_t, (index + 1) << PAGE_SHIFT, end);
 
-		if (folio_test_uptodate(folio)) {
-			folio_lock(folio);
-			if (folio->mapping == mapping)
-				folio_mark_dirty(folio);
-			folio_unlock(folio);
-			folio_put(folio);
-			pos = next;
-			continue;
-		}
+		balance_dirty_pages_ratelimited(mapping);
 
-		/*
-		 * Zero not-uptodate block runs. iomap_zero_range() requires an
-		 * unlocked folio, so recheck ->mapping after each call.
-		 */
-		folio_lock(folio);
-		bpos = pos;
-		while (bpos < next) {
-			loff_t rstart, rend;
-
-			if (folio->mapping != mapping) {
-				folio_unlock(folio);
-				err = iomap_zero_range(inode, bpos, next - bpos,
-						NULL, &exfat_iomap_ops, NULL, NULL);
-				if (err < 0) {
-					folio_put(folio);
-					return err;
-				}
-				folio_lock(folio);
-				break;
-			}
-
-			if (iomap_is_partially_uptodate(folio,
-					offset_in_folio(folio, bpos), blocksize)) {
-				bpos += blocksize;
-				continue;
-			}
+		folio = read_mapping_folio(mapping, index, NULL);
+		if (IS_ERR(folio))
+			return PTR_ERR(folio);
 
-			rstart = bpos;
-			rend = min_t(loff_t, bpos + blocksize, next);
-			while (rend < next &&
-			       !iomap_is_partially_uptodate(folio,
-					offset_in_folio(folio, rend), blocksize))
-				rend = min_t(loff_t, rend + blocksize, next);
-
-			folio_unlock(folio);
-			err = iomap_zero_range(inode, rstart, rend - rstart,
-					NULL, &exfat_iomap_ops, NULL, NULL);
-			if (err < 0) {
-				folio_put(folio);
-				return err;
-			}
-			folio_lock(folio);
-			bpos = rend;
-		}
-
-		/*
-		 * Dirty only a fully uptodate folio. Dirtying a partial folio could
-		 * write uninitialised cache contents over valid on-disk blocks.
-		 */
-		if (folio->mapping == mapping && folio_test_uptodate(folio))
+		folio_lock(folio);
+		if (folio->mapping == mapping) {
 			folio_mark_dirty(folio);
+			pos = next;
+		}
 		folio_unlock(folio);
 		folio_put(folio);
-		pos = next;
 	}
 
 	return 0;
-- 
2.53.0