btrfs: debug patch

btrfs_bio_save_iter() call is ending up corrupting ioend structure.
Why?

fs/btrfs/volumes.c

@@ -6884,13 +6884,30 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 	const enum btrfs_map_op op = btrfs_op(bio);
 	u64 cur_logical = orig_logical;
 	int ret;
+	struct iomap_ioend *ioend = bio->bi_private;
+
+	if (ioend)
+		pr_info("%s: %d ioend: %lx inode %lu %llu/%lu",
+				__func__, __LINE__,
+				(unsigned long)ioend, ioend->io_inode->i_ino,
+				ioend->io_offset, ioend->io_size);
 
 	while (cur_logical < orig_logical + orig_length) {
 		u64 map_length = orig_logical + orig_length - cur_logical;
 		struct btrfs_io_context *bioc = NULL;
 		struct bio *cur_bio;
 
+		if (ioend)
+			pr_info("%s: %d ioend: %lx inode %lu %llu/%lu",
+					__func__, __LINE__,
+					(unsigned long)ioend, ioend->io_inode->i_ino,
+					ioend->io_offset, ioend->io_size);
 		btrfs_bio_save_iter(btrfs_bio(bio));
+		if (ioend)
+			pr_info("%s: %d ioend: %lx inode %lu %llu/%lu",
+					__func__, __LINE__,
+					(unsigned long)ioend, ioend->io_inode->i_ino,
+					ioend->io_offset, ioend->io_size);
 		ret = __btrfs_map_block(fs_info, op, cur_logical, &map_length,
 					&bioc, mirror_num, 1);
 		if (ret)
@@ -6917,6 +6934,11 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 			return errno_to_blk_status(ret);
 		cur_logical += map_length;
 	}
+	if (ioend)
+		pr_info("%s: %d ioend: %lx inode %lu %llu/%lu",
+				__func__, __LINE__,
+				(unsigned long)ioend, ioend->io_inode->i_ino,
+				ioend->io_offset, ioend->io_size);
 	return BLK_STS_OK;
 }