On Sun, 18 Apr 2021 23:54:13 +1000, Michael Ellerman wrote:

RCU complains about us calling printk() from an offline CPU:

  =============================
  WARNING: suspicious RCU usage
  5.12.0-rc7-02874-g7cf90e481cb8 #1 Not tainted
  -----------------------------
  kernel/locking/lockdep.c:3568 RCU-list traversed in non-reader section!!

[...]

Applied to powerpc/next.

[1/1] powerpc/pseries: Stop calling printk in rtas_stop_self()
      https://git.kernel.org/powerpc/c/ed8029d7b472369a010a1901358567ca3b6dbb0d

cheers