linux-kernel - Re: [patch, 2.6.22-rc6] fix nmi

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Message-ID: <467FB7C3.1080206@goop.org>
Date:	Mon, 25 Jun 2007 08:40:35 -0400
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Bj?rn Steinbrink <B.Steinbrink@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [patch, 2.6.22-rc6] fix nmi_watchdog=2 bootup hang

Ingo Molnar wrote:
> * Ingo Molnar <mingo@...e.hu> wrote:
>
>   
>> hm, restoring nmi.c to the v2.6.21 state does not fix the 
>> nmi_watchdog=2 hang. I'll do a bisection run.
>>     
>
> and after spending an hour on 15 bisection steps:
>
>  git-bisect start
>  git-bisect good d1be341dba5521506d9e6dccfd66179080705bea
>  git-bisect bad a06381fec77bf88ec6c5eb6324457cb04e9ffd69
>  git-bisect bad 794543a236074f49a8af89ef08ef6a753e4777e5
>  git-bisect good 24a77daf3d80bddcece044e6dc3675e427eef3f3
>  git-bisect bad ea62ccd00fd0b6720b033adfc9984f31130ce195
>  git-bisect good 7e20ef030dde0e52dd5a57220ee82fa9facbea4e
>  git-bisect bad f19cccf366a07e05703c90038704a3a5ffcb0607
>  git-bisect good 0d08e0d3a97cce22ebf80b54785e00d9b94e1add
>  git-bisect bad 856f44ff4af6e57fdc39a8b2bec498c88438bd27
>  git-bisect bad f8822f42019eceed19cc6c0f985a489e17796ed8
>  git-bisect good 1c3d99c11c47c8a1a9ed6a46555dbf6520683c52
>  git-bisect good b239fb2501117bf3aeb4dd6926edd855be92333d
>  git-bisect good 98de032b681d8a7532d44dfc66aa5c0c1c755a9d
>  git-bisect good 42c24fa22e86365055fc931d833f26165e687c19
>
> the winner is ...
>
>  f8822f42019eceed19cc6c0f985a489e17796ed8 is first bad commit
>  commit f8822f42019eceed19cc6c0f985a489e17796ed8
>  Author: Jeremy Fitzhardinge <jeremy@...p.org>
>  Date:   Wed May 2 19:27:14 2007 +0200
>
>     [PATCH] i386: PARAVIRT: Consistently wrap paravirt ops callsites to make them patchable
>
> ... our wonderful paravirt subsystem, honed to eternal perfection by the 
> testing-machine x86_64 tree.
>
> reverting -git-curr's paravirt.c, paravirt.h, smp.c and tlbflush.h to 
> before the bad commit makes the NMI watchdog work again. Patch against 
> -rc6 is below.
>   

Er, wow.  I've been running with this stuff for months without a 
problem.   Do you have CONFIG_PARAVIRT enabled?  Do you still get the 
hang if you boot with "noreplace-paravirt" to disable the patching? 

Your revert patch seems to take out quite a lot of stuff, some unrelated 
to the paravirt_ops.  Where did that come from?

I presume there's one bad callsite in here which is used by the nmi path 
more or less exclusively.  Is the bug simply that it hangs if you boot 
with nmi_watchdog=2?  ie, no other details?

> @@ -222,10 +211,30 @@ void send_IPI_mask_sequence(cpumask_t ma
>  	 */ 
>  
>  	local_irq_save(flags);
> +
>  	for (query_cpu = 0; query_cpu < NR_CPUS; ++query_cpu) {
>  		if (cpu_isset(query_cpu, mask)) {
> -			__send_IPI_dest_field(cpu_to_logical_apicid(query_cpu),
> -					      vector);
> +		
> +			/*
> +			 * Wait for idle.
> +			 */
> +			apic_wait_icr_idle();
> +		
> +			/*
> +			 * prepare target chip field
> +			 */
> +			cfg = __prepare_ICR2(cpu_to_logical_apicid(query_cpu));
> +			apic_write_around(APIC_ICR2, cfg);
> +		
> +			/*
> +			 * program the ICR 
> +			 */
> +			cfg = __prepare_ICR(0, vector);
> +			
> +			/*
> +			 * Send the IPI. The write to APIC_ICR fires this off.
> +			 */
> +			apic_write_around(APIC_ICR, cfg);
>  		}
>  	}
>  	local_irq_restore(flags);
>   

What's this?  This isn't paravirt_ops related, is it?

    J
-
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