[PATCH v4 07/18] btrfs: attach private to dummy extent buffer pages

[Qu Wenruo <wqu@suse.com>]

Even for regular btrfs, there are locations where we allocate dummy
extent buffers for temporary usage.

Like tree_mod_log_rewind() and get_old_root().

Those dummy extent buffers will be handled by the same eb accessors, and
if they don't have page::private subpage eb accessors can fail.

To address such problems, make __alloc_dummy_extent_buffer() to attach
page private for dummy extent buffers too.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index fb800f237099..7f94f00936d7 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5204,9 +5204,14 @@ struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
 
 	num_pages = num_extent_pages(eb);
 	for (i = 0; i < num_pages; i++) {
+		int ret;
+
 		eb->pages[i] = alloc_page(GFP_NOFS);
 		if (!eb->pages[i])
 			goto err;
+		ret = attach_extent_buffer_page(eb, eb->pages[i], NULL);
+		if (ret < 0)
+			goto err;
 	}
 	set_extent_buffer_uptodate(eb);
 	btrfs_set_header_nritems(eb, 0);
@@ -5214,8 +5219,10 @@ struct extent_buffer *__alloc_dummy_extent_buffer(struct btrfs_fs_info *fs_info,
 
 	return eb;
 err:
-	for (; i > 0; i--)
+	for (; i > 0; i--) {
+		detach_extent_buffer_page(eb, eb->pages[i - 1]);
 		__free_page(eb->pages[i - 1]);
+	}
 	__free_extent_buffer(eb);
 	return NULL;
 }
-- 
2.30.0