linux-kernel - Re: [PATCH] [2/2] Don't complain about disabled irqs when the system has paniced

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Date:	Tue, 02 Sep 2008 16:28:03 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	torvalds@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [2/2] Don't complain about disabled irqs when the
	system has paniced

On Tue, 2008-09-02 at 15:49 +0200, Andi Kleen wrote:
> panic calls smp_send_stop which eventually calls smp_call_function_*.
> smp_call_function warns about disabled interrupts. But it's legal
> to call panic in this case. When this happens panic() prints
> several ugly backtraces. So don't check for disabled interrupts
> in panic state.

While it might be legal for panic to be called from such contexts, I
understand those warnings are there to warn of deadlocks.

So with the below patch you allow panic to deadlock if I understand
things correctly.

> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> 
> Index: linux/kernel/smp.c
> ===================================================================
> --- linux.orig/kernel/smp.c
> +++ linux/kernel/smp.c
> @@ -216,7 +216,7 @@ int smp_call_function_single(int cpu, vo
>  	int err = 0;
>  
>  	/* Can deadlock when called with interrupts disabled */
> -	WARN_ON(irqs_disabled());
> +	WARN_ON(system_state < SYSTEM_PANIC && irqs_disabled());
>  
>  	if (cpu == me) {
>  		local_irq_save(flags);
> @@ -260,7 +260,8 @@ EXPORT_SYMBOL(smp_call_function_single);
>  void __smp_call_function_single(int cpu, struct call_single_data *data)
>  {
>  	/* Can deadlock when called with interrupts disabled */
> -	WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
> +	WARN_ON(system_state < SYSTEM_PANIC &&
> +		(data->flags & CSD_FLAG_WAIT) && irqs_disabled());
>  
>  	generic_exec_single(cpu, data);
>  }
> @@ -329,7 +330,7 @@ int smp_call_function_mask(cpumask_t mas
>  	int slowpath = 0;
>  
>  	/* Can deadlock when called with interrupts disabled */
> -	WARN_ON(irqs_disabled());
> +	WARN_ON(system_state < SYSTEM_PANIC && irqs_disabled());
>  
>  	cpu = smp_processor_id();
>  	allbutself = cpu_online_map;
> --
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