[PATCH] fsdax: force clear dirty mark if CoW

[Shiyang Ruan <ruansy.fnst@fujitsu.com>]

XFS allows CoW on non-shared extents to combat fragmentation[1].  The
old non-shared extent could be mwrited before, its dax entry is marked
dirty.  To be able to delete this entry, clear its dirty mark before
invalidate_inode_pages2_range().

[1] https://lore.kernel.org/linux-xfs/20230321151339.GA11376@frogsfrogsfrogs/

Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
---
 fs/dax.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/fs/dax.c b/fs/dax.c
index 5d2e9b10030e..2ababb89918d 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -781,6 +781,33 @@ static int __dax_invalidate_entry(struct address_space *mapping,
 	return ret;
 }
 
+static int __dax_clear_dirty_range(struct address_space *mapping,
+		pgoff_t start, pgoff_t end)
+{
+	XA_STATE(xas, &mapping->i_pages, start);
+	unsigned int scanned = 0;
+	void *entry;
+
+	xas_lock_irq(&xas);
+	xas_for_each(&xas, entry, end) {
+		entry = get_unlocked_entry(&xas, 0);
+		xas_clear_mark(&xas, PAGECACHE_TAG_DIRTY);
+		xas_clear_mark(&xas, PAGECACHE_TAG_TOWRITE);
+		put_unlocked_entry(&xas, entry, WAKE_NEXT);
+
+		if (++scanned % XA_CHECK_SCHED)
+			continue;
+
+		xas_pause(&xas);
+		xas_unlock_irq(&xas);
+		cond_resched();
+		xas_lock_irq(&xas);
+	}
+	xas_unlock_irq(&xas);
+
+	return 0;
+}
+
 /*
  * Delete DAX entry at @index from @mapping.  Wait for it
  * to be unlocked before deleting it.
@@ -1440,6 +1467,16 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
 	 * written by write(2) is visible in mmap.
 	 */
 	if (iomap->flags & IOMAP_F_NEW || cow) {
+		/*
+		 * Filesystem allows CoW on non-shared extents. The src extents
+		 * may have been mmapped with dirty mark before. To be able to
+		 * invalidate its dax entries, we need to clear the dirty mark
+		 * in advance.
+		 */
+		if (cow)
+			__dax_clear_dirty_range(iomi->inode->i_mapping,
+						pos >> PAGE_SHIFT,
+						(end - 1) >> PAGE_SHIFT);
 		invalidate_inode_pages2_range(iomi->inode->i_mapping,
 					      pos >> PAGE_SHIFT,
 					      (end - 1) >> PAGE_SHIFT);
-- 
2.39.2