kgdb: fix NMI hangs

This patch fixes the hang regression with kgdb when the NMI interrupt
comes in while the master core is returning from an exception.

Adjust the NMI logic such that KGDB will not stop NMI exceptions from
occurring by in general returning NOTIFY_DONE.  It is not possible to
distinguish the debug NMI sync vs the normal NMI apic interrupt so
kgdb needs to catch the unknown NMI if it the debugger was previously
active on one of the cpus.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 3 deletions

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 37194d6374d8..5d7a21119bf8 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -41,6 +41,7 @@
 #include <linux/kgdb.h>
 #include <linux/init.h>
 #include <linux/smp.h>
+#include <linux/nmi.h>
 
 #include <asm/apicdef.h>
 #include <asm/system.h>
@@ -290,6 +291,8 @@ single_step_cont(struct pt_regs *regs, struct die_args *args)
         return NOTIFY_STOP;
 }
 
+static int was_in_debug_nmi[NR_CPUS];
+
 static int __kgdb_notify(struct die_args *args, unsigned long cmd)
 {
         struct pt_regs *regs = args->regs;
@@ -299,15 +302,24 @@ static int __kgdb_notify(struct die_args *args, unsigned long cmd)
                 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();
                         return NOTIFY_STOP;
                 }
                 return NOTIFY_DONE;
 
         case DIE_NMI_IPI:
                 if (atomic_read(&kgdb_active) != -1) {
-                        /* KGDB CPU roundup: */
-                        if (kgdb_nmicallback(raw_smp_processor_id(), regs))
-                                return NOTIFY_DONE;
+                        /* KGDB CPU roundup */
+                        kgdb_nmicallback(raw_smp_processor_id(), regs);
+                        was_in_debug_nmi[raw_smp_processor_id()] = 1;
+                        touch_nmi_watchdog();
+                }
+                return NOTIFY_DONE;
+
+        case DIE_NMIUNKNOWN:
+                if (was_in_debug_nmi[raw_smp_processor_id()]) {
+                        was_in_debug_nmi[raw_smp_processor_id()] = 0;
                         return NOTIFY_STOP;
                 }
                 return NOTIFY_DONE;