[PATCH 6.7 613/713] bcachefs: check for failure to downgrade

[Sasha Levin]

From: Kent Overstreet <kent.overstreet@xxxxxxxxx>

commit 447c1c01051251853e851bd77f26546488cbc7b7 upstream.

With the upcoming member seq patch, it's now critical that we don't ever
write to a superblock that hasn't been version downgraded - failure to
update member seq fields will cause split brain detection to fire
erroniously.

Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/bcachefs/errcode.h  |  1 +
 fs/bcachefs/super-io.c | 12 ++++++++++++
 2 files changed, 13 insertions(+)

diff --git a/fs/bcachefs/errcode.h b/fs/bcachefs/errcode.h
index 9ce29681eec96..ac90faccdcb22 100644
--- a/fs/bcachefs/errcode.h
+++ b/fs/bcachefs/errcode.h
@@ -224,6 +224,7 @@
 	x(BCH_ERR_invalid,		invalid_bkey)				\
 	x(BCH_ERR_operation_blocked,    nocow_lock_blocked)			\
 	x(EIO,				btree_node_read_err)			\
+	x(EIO,				sb_not_downgraded)			\
 	x(BCH_ERR_btree_node_read_err,	btree_node_read_err_fixable)		\
 	x(BCH_ERR_btree_node_read_err,	btree_node_read_err_want_retry)		\
 	x(BCH_ERR_btree_node_read_err,	btree_node_read_err_must_retry)		\
diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
index 4c98d8cc2a797..6405cc1d651fd 100644
--- a/fs/bcachefs/super-io.c
+++ b/fs/bcachefs/super-io.c
@@ -966,6 +966,18 @@ int bch2_write_super(struct bch_fs *c)
 	if (!BCH_SB_INITIALIZED(c->disk_sb.sb))
 		goto out;
 
+	if (le16_to_cpu(c->disk_sb.sb->version) > bcachefs_metadata_version_current) {
+		struct printbuf buf = PRINTBUF;
+		prt_printf(&buf, "attempting to write superblock that wasn't version downgraded (");
+		bch2_version_to_text(&buf, le16_to_cpu(c->disk_sb.sb->version));
+		prt_str(&buf, " > ");
+		bch2_version_to_text(&buf, bcachefs_metadata_version_current);
+		prt_str(&buf, ")");
+		bch2_fs_fatal_error(c, "%s", buf.buf);
+		printbuf_exit(&buf);
+		return -BCH_ERR_sb_not_downgraded;
+	}
+
 	for_each_online_member(ca, c, i) {
 		__set_bit(ca->dev_idx, sb_written.d);
 		ca->sb_write_error = 0;
-- 
2.43.0