From: Drew Moseley <dmoseley@mvista.com>
Organization: Monta Vista Software
To: Keith Owens <kaos@ocs.com.au>
Subject: Re: Unnecessary warnings in smp_send_stop on i386 arch.
Date: Wed, 17 May 2006 11:34:57 -0700
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On Tuesday 16 May 2006 9:56 pm, Keith Owens wrote:
> Drew Moseley (on Tue, 16 May 2006 19:43:05 -0700) wrote:
...
> >
> >I modified the i386/kernel/smp.c file to be functionally equivalent to the
> >x86_64/kernel/smp.c file to address this issue.
> >
...
>
> NAK this patch.  There is a real potential deadlock if you call
> smp_call_function() with interrupts disabled, it has caused kernel
> hangs in the past.  This patch removes the check for the potential
> deadlock and will allow bad code to creep back into the kernel.  See
> http://lkml.org/lkml/2004/5/2/116.  I find it quite disturbing that
> x86_64 has removed that check :(

So presumably the warn_on() call should be added back to the x86_64 arch?
Does that mean that the comment in the current code 
	* You must not call this function with disabled interrupts or from a
	* hardware interrupt handler or from a bottom half handler.
	* Actually there are a few legal cases, like panic.
is incorrect?

I did manage to find this thread; http://lkml.org/lkml/2004/12/2/209; which 
seems related..

Does is sound reasonable then to call local_irq_enable() for the scenarios 
where this will occur?  Specifically, any call to smp_send_stop() where IRQ's 
might be disabled may need that call to eliminate the deadlock opportunity.  
Or am I just plain confused?

Drew
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