The patch titled Subject: panic: fix the panic_print NMI backtrace setting has been added to the -mm mm-hotfixes-unstable branch. Its filename is panic-fixes-the-panic_print-nmi-backtrace-setting.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: "Guilherme G. Piccoli" gpiccoli@igalia.com Subject: panic: fix the panic_print NMI backtrace setting Date: Sun, 26 Feb 2023 13:08:38 -0300

Commit 8d470a45d1a6 ("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: 8d470a45d1a6 ("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 ---

--- a/kernel/panic.c~panic-fixes-the-panic_print-nmi-backtrace-setting +++ b/kernel/panic.c @@ -212,9 +212,6 @@ static void panic_print_sys_info(bool console_flush) return; }

- if (panic_print & PANIC_PRINT_ALL_CPU_BT) - trigger_all_cpu_backtrace(); - if (panic_print & PANIC_PRINT_TASK_INFO) show_state();

@@ -244,6 +241,30 @@ void check_panic_on_warn(const char *origin) origin, limit); }

+/* + * Helper that triggers the NMI backtrace (if set in panic_print) + * and then performs the secondary CPUs shutdown - we cannot have + * the NMI backtrace after the CPUs are off! + */ +static void panic_other_cpus_shutdown(bool crash_kexec) +{ + if (panic_print & PANIC_PRINT_ALL_CPU_BT) + trigger_all_cpu_backtrace(); + + /* + * Note that smp_send_stop() is the usual SMP shutdown function, + * which unfortunately may not be hardened to work in a panic + * situation. If we want to do crash dump after notifier calls + * and kmsg_dump, we will need architecture dependent extra + * bits in addition to stopping other CPUs, hence we rely on + * crash_smp_send_stop() for that. + */ + if (!crash_kexec) + smp_send_stop(); + else + crash_smp_send_stop(); +} + /** * panic - halt the system * @fmt: The text string to print @@ -334,23 +355,10 @@ void panic(const char *fmt, ...) * * Bypass the panic_cpu check and call __crash_kexec directly. */ - if (!_crash_kexec_post_notifiers) { + if (!_crash_kexec_post_notifiers) __crash_kexec(NULL);

- /* - * Note smp_send_stop is the usual smp shutdown function, which - * unfortunately means it may not be hardened to work in a - * panic situation. - */ - smp_send_stop(); - } else { - /* - * If we want to do crash dump after notifier calls and - * kmsg_dump, we will need architecture dependent extra - * works in addition to stopping other CPUs. - */ - crash_smp_send_stop(); - } + panic_other_cpus_shutdown(_crash_kexec_post_notifiers);

/* * Run any panic handlers, including those that might need to _

Patches currently in -mm which might be from gpiccoli@igalia.com are

panic-fixes-the-panic_print-nmi-backtrace-setting.patch