nmi VS cpu hotplug

PATCH In review Shaohua Li 2 participants 2 messages Dec 1, 2005

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Shaohua Li

author

2005-12-01 02:24 UTC #0 lore raw

PATCH 1/1 nmi VS cpu hotplug

Hi,
With CPU hotplug enabled, NMI watchdog stoped working. It appears the violation is the cpu_online check in nmi handler. local ACPI based NMI watchdog is initialized before we set CPU online for APs. It's quite possible a NMI is fired before we set CPU online, and that's what happens here.
Zwane, I suppose you saw nmi interrupts on offline CPU, so you added this one. Several days ago I sent a patch titled 'disable LAPIC completely for offline CPU', which I guess will make it disappear. Can you try it?
So the solution is either to initialize nmi later or to delete the cpu_online check. I just take what x86_64 does.

Signed-off-by Shaohua Li <[email protected]>

---

 linux-2.6.14-root/arch/i386/kernel/traps.c |    7 -------
 1 files changed, 7 deletions(-)

arch/i386/kernel/traps.c renamed from arch/i386/kernel/traps.c~nmi-cpuhotplug +0 -7

diff -puN arch/i386/kernel/traps.c~nmi-cpuhotplug arch/i386/kernel/traps.c
@@ -650,13 +650,6 @@ fastcall void do_nmi(struct pt_regs * re
 
 	cpu = smp_processor_id();
 
-#ifdef CONFIG_HOTPLUG_CPU
-	if (!cpu_online(cpu)) {
-		nmi_exit();
-		return;
-	}
-#endif
-
 	++nmi_count(cpu);
 
 	if (!rcu_dereference(nmi_callback)(regs, cpu))

Zwane Mwaikambo

2005-12-01 02:48 UTC #1 lore raw

Quoted 14 lines · Shaohua Li

Hi,
With CPU hotplug enabled, NMI watchdog stoped working. It appears the violation is the cpu_online check in nmi handler. local ACPI based NMI watchdog is initialized before we set CPU online for APs. It's quite possible a NMI is fired before we set CPU online, and that's what happens here.
Zwane, I suppose you saw nmi interrupts on offline CPU, so you added this one. Several days ago I sent a patch titled 'disable LAPIC completely for offline CPU', which I guess will make it disappear. Can you try it?
So the solution is either to initialize nmi later or to delete the cpu_online check. I just take what x86_64 does.

Quoted 1 line

Signed-off-by Shaohua Li <[email protected]>

Signed-off-by Zwane Mwaikambo <[email protected]>

Quoted 9 lines

---
 linux-2.6.14-root/arch/i386/kernel/traps.c |    7 -------
 1 files changed, 7 deletions(-)
diff -puN arch/i386/kernel/traps.c~nmi-cpuhotplug arch/i386/kernel/traps.c

arch/i386/kernel/traps.c fastcall void do_nmi(struct pt_regs * re · line 658

Quoted 9 lines

arch/i386/kernel/traps.c renamed from arch/i386/kernel/traps.c~nmi-cpuhotplug +0 -6

@@ -650,13 +650,6 @@ fastcall void do_nmi(struct pt_regs * re
 
 	cpu = smp_processor_id();
 
-#ifdef CONFIG_HOTPLUG_CPU
-	if (!cpu_online(cpu)) {
-		nmi_exit();
-		return;
-	}
-#endif

Nice catch, well that's really old debug code for the 'toy' i386 hotplug code i'm fine with deleting it.

Thanks,
Zwane