linux-kernel - Re: [PATCH] x86, UV: Fix NMI handler for UV platforms

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Message-ID: <20110321161425.GC23614@elte.hu>
Date:	Mon, 21 Mar 2011 17:14:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jack Steiner <steiner@....com>
Cc:	tglx@...utronix.de, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Cyrill Gorcunov <gorcunov@...il.com>
Subject: Re: [PATCH] x86, UV: Fix NMI handler for UV platforms


* Jack Steiner <steiner@....com> wrote:

> This fixes a problem seen on UV systems handling NMIs from the node controller.
> The original code used the DIE notifier as the hook to get to the UV NMI
> handler. This does not work if performance counters are active - the hw_perf
> code consumes the NMI and the UV handler is not called.

Sigh:

> --- linux.orig/arch/x86/kernel/traps.c	2011-03-21 09:05:43.000000000 -0500
> +++ linux/arch/x86/kernel/traps.c	2011-03-21 09:13:01.306555675 -0500
> @@ -57,6 +57,7 @@
>  #include <asm/mce.h>
>  
>  #include <asm/mach_traps.h>
> +#include <asm/uv/uv.h>
>  
>  #ifdef CONFIG_X86_64
>  #include <asm/x86_init.h>
> @@ -397,13 +398,16 @@ unknown_nmi_error(unsigned char reason,
>  static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
>  {
>  	unsigned char reason = 0;
> +	int handled;
>  
>  	/*
>  	 * CPU-specific NMI must be processed before non-CPU-specific
>  	 * NMI, otherwise we may lose it, because the CPU-specific
>  	 * NMI can not be detected/processed on other CPUs.
>  	 */
> -	if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
> +	handled = uv_handle_nmi(regs, reason);
> +	if (notify_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP ||
> +	    		handled)
>  		return;

Such code is extremely ugly. Please *reduce* the number of is_uv_system() type 
of hacks in core x86 code, not increase it!

Any reason why a higher priority for the UV NMI handler cannot solve the 'perf 
eats the NMI' problem?

Thanks,

	Ingo
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