[PATCH] NMI watchdog config option (was: Re: [PATCH] NMI lockup and AltSysRq-P dumping calltraces on _all_ cpus via NMI IPI)

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against 2.6.12-rc4

This patch adds dumping of calltraces on _all_ CPUs
on AltSysRq-P and NMI LOCKUP. It does this via sending
NMI IPI interrupts to the cpus.

I saw the same patch in RedHat kernels, here goes our own version of the patch, not sure it will be accepted, but I think it can be used by some people at least for debugging lockups etc.



I'd done a similar thing, but just using smp_call_function (I hacked the
interrupt routine to fish pt_regs back out, and override *info in some
cases). Doing NMIs, as you've done, is probably nicer, but a lot more
work.
Yes, but it catches _all_ calltraces which is very important, espicially when you do not have NMI watchdog enabled.
BTW, why NMI watchdog is disabled by default? We constantly making it on by default in our kernels and had no problems with it. 
I send a patch attached which tunes NMI watchdog by config option...


The problem with it (and my patch too) is that you're hooking into arch
specific code from generic code, which means you'll break every other
arch apart from i386. Fixing this is a pain in the rear end, but would
be needed to merge the patch. OTOH, the patch is extremely useful, so
would be nice to fix if you have the energy ...

Well, I used #idef __i386__ to not break generic code for other archs.
I have no any other hardware except for i386+, so it is almost impossible for me to make this code work on other archs. I think people who are interested in this functionality will provide the required code later. 

Kirill

--- ./arch/i386/Kconfig.debug.nmiwd	2005-05-10 16:09:57.000000000 +0400
+++ ./arch/i386/Kconfig.debug	2005-05-17 10:49:03.000000000 +0400
@@ -59,6 +59,14 @@ config 4KSTACKS
 	  on the VM subsystem for higher order allocations. This option
 	  will also use IRQ stacks to compensate for the reduced stackspace.
 
+config NMI_WATCHDOG
+	bool "NMI Watchdog"
+	default y
+	help
+	  If you say Y here the kernel will activate NMI watchdog by default
+	  on boot. You can still activate NMI watchdog via nmi_watchdog
+	  command line option even if you say N here.
+
 config X86_FIND_SMP_CONFIG
 	bool
 	depends on X86_LOCAL_APIC || X86_VOYAGER
--- ./arch/i386/kernel/nmi.c.nmiwd	2005-05-10 18:20:00.000000000 +0400
+++ ./arch/i386/kernel/nmi.c	2005-05-17 10:47:38.000000000 +0400
@@ -34,7 +34,12 @@
 
 #include "mach_traps.h"
 
-unsigned int nmi_watchdog = NMI_NONE;
+#ifdef CONFIG_NMI_WATCHDOG
+#define NMI_DEFAULT NMI_IO_APIC
+#else
+#define NMI_DEFAULT NMI_NONE
+#endif
+unsigned int nmi_watchdog = NMI_DEFAULT;
 extern int unknown_nmi_panic;
 static unsigned int nmi_hz = HZ;
 static unsigned int nmi_perfctr_msr;	/* the MSR to reset in NMI handler */
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