diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 2f1df6e29d4a..822317364065 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1614,12 +1614,14 @@ static noinline_for_stack int extent_writepage_io(struct btrfs_inode *inode,
 	       start + len <= folio_start + folio_size(folio));
 
 	ret = btrfs_writepage_cow_fixup(folio);
-	if (ret) {
+	if (ret == -EAGAIN) {
 		/* Fixup worker will requeue */
 		folio_redirty_for_writepage(bio_ctrl->wbc, folio);
 		folio_unlock(folio);
 		return 1;
 	}
+	if (ret < 0)
+		return ret;
 
 	for (cur = start; cur < start + len; cur += fs_info->sectorsize)
 		set_bit((cur - folio_start) >> fs_info->sectorsize_bits, &range_bitmap);
@@ -1724,6 +1726,30 @@ static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl
 	 * The proper bitmap can only be initialized until writepage_delalloc().
 	 */
 	bio_ctrl->submit_bitmap = (unsigned long)-1;
+
+	/*
+	 * If the page is dirty but without private set, it's marked dirty
+	 * without informing the fs.
+	 * Nowadays that is a bug, since the introduction of
+	 * pin_user_pages*().
+	 *
+	 * So here we check if the page has private set to rule out such
+	 * case.
+	 * But we also have a long history of relying on the COW fixup,
+	 * so here we only enable this check for experimental builds until
+	 * we're sure it's safe.
+	 */
+	if (IS_ENABLED(CONFIG_BTRFS_EXPERIMENTAL) &&
+	    unlikely(!folio_test_private(folio))) {
+		WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
+		btrfs_err_rl(fs_info,
+	"root %lld ino %llu folio %llu is marked dirty without notifying the fs",
+			     inode->root->root_key.objectid,
+			     btrfs_ino(inode), folio_pos(folio));
+		ret = -EUCLEAN;
+		goto done;
+	}
+
 	ret = set_folio_extent_mapped(folio);
 	if (ret < 0)
 		goto done;
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index da763a61d4a7..84a6f764f28b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2879,6 +2879,21 @@ int btrfs_writepage_cow_fixup(struct folio *folio)
 	if (folio_test_ordered(folio))
 		return 0;
 
+	/*
+	 * For experimental build, we error out instead of EAGAIN.
+	 *
+	 * We should not hit such out-of-band dirty folios anymore.
+	 */
+	if (IS_ENABLED(CONFIG_BTRFS_EXPERIMENTAL)) {
+		WARN_ON(IS_ENABLED(CONFIG_BTRFS_DEBUG));
+		btrfs_err_rl(fs_info,
+	"root %lld ino %llu folio %llu is marked dirty without notifying the fs",
+			     BTRFS_I(inode)->root->root_key.objectid,
+			     btrfs_ino(BTRFS_I(inode)),
+			     folio_pos(folio));
+		return -EUCLEAN;
+	}
+
 	/*
 	 * folio_checked is set below when we create a fixup worker for this
 	 * folio, don't try to create another one if we're already