bcachefs: Ensure superblock gets written when we go ERO

When we go emergency read-only, make sure we do a final write_super() to
persist counters and error counts - this can be critical for piecing
together what fsck was doing.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

fs/bcachefs/super.c

@@ -377,6 +377,11 @@ void bch2_fs_read_only(struct bch_fs *c)
 		bch_verbose(c, "marking filesystem clean");
 		bch2_fs_mark_clean(c);
 	} else {
+		/* Make sure error counts/counters are persisted */
+		mutex_lock(&c->sb_lock);
+		bch2_write_super(c);
+		mutex_unlock(&c->sb_lock);
+
 		bch_verbose(c, "done going read-only, filesystem not clean");
 	}
 }