panic: fix the panic_print NMI backtrace setting

Commit 8d470a45 ("panic: add option to dump all CPUs backtraces in
panic_print") introduced a setting for the "panic_print" kernel parameter
to allow users to request a NMI backtrace on panic.  Problem is that the
panic_print handling happens after the secondary CPUs are already
disabled, hence this option ended-up being kind of a no-op - kernel skips
the NMI trace in idling CPUs, which is the case of offline CPUs.

Fix it by checking the NMI backtrace bit in the panic_print prior to the
CPU disabling function.

Link: https://lkml.kernel.org/r/20230226160838.414257-1-gpiccoli@igalia.com


Fixes: 8d470a45 ("panic: add option to dump all CPUs backtraces in panic_print")
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Cc: <stable@vger.kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Michael Kelley <mikelley@microsoft.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>