[git pull] kgdb 2.6.27-rc8 fixes

[git pull] kgdb 2.6.27-rc8 fixes

[Jason Wessel]

Linus, please pull the kgdb git tree fixes for 2.6.27-rc8

  git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/linux-2.6-kgdb.git for_linus

Summary: 

Testing the kgdb with kvm has found 2 problems:
 - NMI code has a race where it can be invoked twice
 - The softlockup watchdog must be touched when running
   with CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE=1, else
   the kernel executes a reboot if debugged for too long.
   

Short log follows:

--- 

Jan Kiszka (1):
      kgdb, x86: Avoid invoking kgdb_nmicallback twice per NMI

Jason Wessel (1):
      kgdb: call touch_softlockup_watchdog on resume

 arch/x86/kernel/kgdb.c |    7 +------
 kernel/kgdb.c          |    3 +++
 2 files changed, 4 insertions(+), 6 deletions(-)

[PATCH 1/2] kgdb, x86: Avoid invoking kgdb_nmicallback twice per NMI

[Jason Wessel]

From: Jan Kiszka <jan.kiszka@siemens.com>

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>
---
 arch/x86/kernel/kgdb.c |    7 +------
 1 files changed, 1 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 8282a21..10435a1 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:
-- 
1.6.0.2

[PATCH 2/2] kgdb: call touch_softlockup_watchdog on resume

[Jason Wessel]

The softlockup watchdog needs to be touched when resuming the from the
kgdb stopped state to avoid the printk that a CPU is stuck if the
debugger was active for longer than the softlockup threshold.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
 kernel/kgdb.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 25d955d..e4dcfb2 100644
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -590,6 +590,7 @@ static void kgdb_wait(struct pt_regs *regs)
 
 	/* Signal the primary CPU that we are done: */
 	atomic_set(&cpu_in_kgdb[cpu], 0);
+	touch_softlockup_watchdog();
 	clocksource_touch_watchdog();
 	local_irq_restore(flags);
 }
@@ -1432,6 +1433,7 @@ acquirelock:
 	    atomic_read(&kgdb_cpu_doing_single_step) != cpu) {
 
 		atomic_set(&kgdb_active, -1);
+		touch_softlockup_watchdog();
 		clocksource_touch_watchdog();
 		local_irq_restore(flags);
 
@@ -1524,6 +1526,7 @@ acquirelock:
 kgdb_restore:
 	/* Free kgdb_active */
 	atomic_set(&kgdb_active, -1);
+	touch_softlockup_watchdog();
 	clocksource_touch_watchdog();
 	local_irq_restore(flags);
 
-- 
1.6.0.2