[PATCH] f2fs: fix to avoid potential deadloop in f2fs_fsync_node_pages()

[PATCH] f2fs: fix to avoid potential deadloop in f2fs_fsync_node_pages()

[Chao Yu]

There is potential deadloop in race condition:

Thread A				Thread B
- fsync
 - f2fs_do_sync_file
  - f2fs_fsync_node_pages
   - last_fsync_dnode
    - folio_get(last_folio)
					- f2fs_setattr
					 - f2fs_truncate
					  - f2fs_truncate_blocks
					   - f2fs_do_truncate_blocks
					    - f2fs_truncate_inode_blocks
					     - truncate_dnode
					      - truncate_node
					       - invalidate_mapping_pages
					        - folio->mapping = NULL
   - is_node_folio alwasy return false
   - atomic && !marked is always true,
     then goto retry

Cc: stable@kernel.org
Fixes: 608514deba38 ("f2fs: set fsync mark only for the last dnode")
Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/f2fs/node.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 968e5ed38816..86c2e67e43b6 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -2016,6 +2016,11 @@ int f2fs_fsync_node_pages(struct f2fs_sb_info *sbi, struct inode *inode,
 		f2fs_debug(sbi, "Retry to write fsync mark: ino=%u, idx=%lx",
 			   ino, last_folio->index);
 		folio_lock(last_folio);
+		if (unlikely(!is_node_folio(last_folio))) {
+			f2fs_folio_put(last_folio, true);
+			ret = -EAGAIN;
+			goto out;
+		}
 		f2fs_folio_wait_writeback(last_folio, NODE, true, true);
 		folio_mark_dirty(last_folio);
 		folio_unlock(last_folio);
-- 
2.49.0