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.

Fixes: 8d470a45d1a6 ("panic: add option to dump all CPUs backtraces in panic_print") Cc: stable@vger.kernel.org Signed-off-by: Guilherme G. Piccoli gpiccoli@igalia.com ---

V5: - Kept the local version of "crash_kexec_post_notifiers", since this is standalone fix that should be backported to stable. Hence, it's not a good idea to mess with it in this patch (thanks Andrew!).

V4: - Sent as standalone patch, rebased against v6.2-rc7. - Link: https://lore.kernel.org/lkml/20230210203510.1734835-1-gpiccoli@igalia.com/

kernel/panic.c | 44 ++++++++++++++++++++++++++------------------ 1 file changed, 26 insertions(+), 18 deletions(-)

diff --git a/kernel/panic.c b/kernel/panic.c index 463c9295bc28..e026191a0a07 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -211,9 +211,6 @@ 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();

@@ -243,6 +240,30 @@ 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 @@ -333,23 +354,10 @@ 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