kgdb, x86: Avoid invoking kgdb_nmicallback twice per NMI

Stress-testing KVM's latest NMI support with kgdbts inside an SMP guest,
I came across spurious unhandled NMIs while running the singlestep test.
Looking closer at the code path each NMI takes when KGDB is enabled, I
noticed that kgdb_nmicallback is called twice per event: One time via
DIE_NMI_IPI notification, the second time on DIE_NMI. Removing the first
invocation cures the unhandled NMIs here.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 1 insertions, 6 deletions

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 8282a2139681..10435a120d22 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -455,12 +455,7 @@ static int __kgdb_notify(struct die_args *args, unsigned long cmd)
                 return NOTIFY_DONE;
 
         case DIE_NMI_IPI:
-                if (atomic_read(&kgdb_active) != -1) {
-                        /* KGDB CPU roundup */
-                        kgdb_nmicallback(raw_smp_processor_id(), regs);
-                        was_in_debug_nmi[raw_smp_processor_id()] = 1;
-                        touch_nmi_watchdog();
-                }
+                /* Just ignore, we will handle the roundup on DIE_NMI. */
                 return NOTIFY_DONE;
 
         case DIE_NMIUNKNOWN: