ring-buffer: Fix buffer locking in ring_buffer_subbuf_order_set()

Enlarge the critical section in ring_buffer_subbuf_order_set() to
ensure that error handling takes place with per-buffer mutex held,
thus preventing list corruption and other concurrency-related issues.

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
Link: https://lore.kernel.org/20250606112242.1510605-1-dmantipov@yandex.ru


Reported-by:  <syzbot+05d673e83ec640f0ced9@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=05d673e83ec640f0ced9


Fixes: f9b94daa ("ring-buffer: Set new size of the ring buffer sub page")
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>