f2fs: fix fs corruption due to zero inode page

This patch fixes the following scenario.

- f2fs_create/f2fs_mkdir             - write_checkpoint
 - f2fs_mark_inode_dirty_sync         - block_operations
                                       - f2fs_lock_all
                                       - f2fs_sync_inode_meta
                                        - f2fs_unlock_all
                                        - sync_inode_metadata
 - f2fs_lock_op
                                         - f2fs_write_inode
                                          - update_inode_page
                                           - get_node_page
                                             return -ENOENT
 - new_inode_page
  - fill_node_footer
 - f2fs_mark_inode_dirty_sync
 - ...
 - f2fs_unlock_op
                                          - f2fs_inode_synced
                                       - f2fs_lock_all
                                       - do_checkpoint

In this checkpoint, we can get an inode page which contains zeros having valid
node footer only.

Cc: <stable@vger.kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 2520fa7..0900814 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -316,7 +316,6 @@ int update_inode_page(struct inode *inode)
 		} else if (err != -ENOENT) {
 			f2fs_stop_checkpoint(sbi, false);
 		}
-		f2fs_inode_synced(inode);
 		return 0;
 	}
 	ret = update_inode(inode, node_page);
@@ -450,6 +449,7 @@ void handle_failed_inode(struct inode *inode)
 	 * in a panic when flushing dirty inodes in gdirty_list.
 	 */
 	update_inode_page(inode);
+	f2fs_inode_synced(inode);
 
 	/* don't make bad inode, since it becomes a regular file. */
 	unlock_new_inode(inode);