Re: [PATCH] NMI watch dog notify patch

From: Keith Owens
Date: Fri Jul 29 2005 - 00:11:39 EST

On Thu, 28 Jul 2005 21:16:56 -0700,
George Anzinger <george@xxxxxxxxxx> wrote:
>Keith Owens wrote:
>> On Thu, 28 Jul 2005 13:31:58 -0700,
>> George Anzinger <george@xxxxxxxxxx> wrote:
>>>I have been doing some work on kgdb to pull a few of it "fingers" out of
>>>various places in the kernel. This is the final location where we have
>>>a kgdb intercept not covered by a notify.
>> I like the idea, but the hook should be in die_nmi(), not in the
>> watchdog, using the reason that is already passed into die_nmi.
>> die_nmi() is also called for a real NMI.
>I had though that too, but it does not allow recovery (i.e. lets reset
>the watchdog and try again).

die_nmi() returns to nmi_watchdog_tick(), nmi_watchdog_tick does the
reset and continues. Patch below.

>Hmm.. just looked at traps.c. Seems die_nmi is NOT called from the nmi
>trap, only from the watchdog. Also, there is a notify in the path to
>the other nmi stuff.

I was looking at unknown_nmi_panic_callback(), which also calls

traps.c already has several notify_die() calls, nmi.c has none. It is
cleaner to keep all the notification in traps.c, with this small change
to nmi.c to cope with die_nmi() returning.

Index: linux/arch/i386/kernel/nmi.c
--- linux.orig/arch/i386/kernel/nmi.c 2005-07-28 17:22:06.735038510 +1000
+++ linux/arch/i386/kernel/nmi.c 2005-07-29 15:19:00.371196596 +1000
@@ -494,8 +494,10 @@ void nmi_watchdog_tick (struct pt_regs *
* wait a few IRQs (5 seconds) before doing the oops ...
- if (alert_counter[cpu] == 5*nmi_hz)
+ if (alert_counter[cpu] == 5*nmi_hz) {
die_nmi(regs, "NMI Watchdog detected LOCKUP");
+ alert_counter[cpu] = 0;
+ }
} else {
last_irq_sums[cpu] = sum;
alert_counter[cpu] = 0;

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