panic: fix the panic_print NMI backtrace setting

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>

diff --git a/kernel/panic.c b/kernel/panic.c
index 487f5b0..5cfea83 100644 (file)
--- a/kernel/panic.c
+++ 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