Re: [patch] disable NMI watchdog by default

Len Brown
2007-03-05T17:50:40Z

On Monday 05 March 2007 07:20, Ingo Molnar wrote:
>
> Linus,
>
> Andrew sent the patch below (which is now months old and has been in -mm
> for some time) towards Andi's tree 4 weeks ago, but apparently it fell
> into a black hole there - the patch is still not upstream!
>
> This is a must-have for v2.6.21

I agree.
There are multiple machines not booting because of nmi_watchdog.
Some of them are documented here:
http://bugzilla.kernel.org/show_bug.cgi?id=7839

We used to think this was the "nolapic" bug,
but it is actually the "nmi_watchdog=0" bug.

-Len

> Frankly, i find it ridiculous that i had to write more than 10 emails
> about this stupid topic already, while i'm the original author of this
> feature to begin with. The "do not enable by default debug features that
> break certain systems" concept is obvious to me.
>
> This category of regressions has been introduced by Andi when he made
> the NMI watchdog the default in certain scenarios at around v2.6.18 -
> over my repeated objections. Andi Cc:-ed :-)
>
> Ingo
>
> ----- Forwarded message from Ingo Molnar <mingo@elte.hu> -----
>
> From: Ingo Molnar <mingo@elte.hu>
> Subject: [patch] disable NMI watchdog by default
>
> there's a new NMI watchdog related problem: KVM crashes on certain
> bzImages because ... we enable the NMI watchdog by default (even if the
> user does not ask for it) , and no other OS on this planet does that so
> KVM doesnt have emulation for that yet. So KVM injects a #GP, which
> crashes the Linux guest:
>
> general protection fault: 0000 [#1]
> PREEMPT SMP
> Modules linked in:
> CPU: 0
> EIP: 0060:[<c011a8ae>] Not tainted VLI
> EFLAGS: 00000246 (2.6.20-rc5-rt0 #3)
> EIP is at setup_apic_nmi_watchdog+0x26d/0x3d3
>
> and no, i did /not/ request an nmi_watchdog on the boot command line!
>
> Solution: turn off that darn thing! It's a debug tool, not a 'make life
> harder' tool!!
>
> with this patch the KVM guest boots up just fine.
>
> And with this my laptop (Lenovo T60) also stopped its sporadic hard
> hanging (sometimes in acpi_init(), sometimes later during bootup,
> sometimes much later during actual use) as well. It hung with both
> nmi_watchdog=1 and nmi_watchdog=2, so it's generally the fact of NMI
> injection that is causing problems, not the NMI watchdog variant, nor
> any particular bootup code.
>
> The patch is unintrusive.
>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
>
> Index: linux/include/asm-i386/nmi.h
> ===================================================================
> --- linux.orig/include/asm-i386/nmi.h
> +++ linux/include/asm-i386/nmi.h
> @@ -33,7 +33,7 @@ extern int nmi_watchdog_tick (struct pt_
>
> extern atomic_t nmi_active;
> extern unsigned int nmi_watchdog;
> -#define NMI_DEFAULT -1
> +#define NMI_DEFAULT 0
> #define NMI_NONE 0
> #define NMI_IO_APIC 1
> #define NMI_LOCAL_APIC 2
> Index: linux/include/asm-x86_64/nmi.h
> ===================================================================
> --- linux.orig/include/asm-x86_64/nmi.h
> +++ linux/include/asm-x86_64/nmi.h
> @@ -63,7 +63,7 @@ extern int setup_nmi_watchdog(char *);
>
> extern atomic_t nmi_active;
> extern unsigned int nmi_watchdog;
> -#define NMI_DEFAULT -1
> +#define NMI_DEFAULT 0
> #define NMI_NONE 0
> #define NMI_IO_APIC 1
> #define NMI_LOCAL_APIC 2
>
> -
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