linux-kernel - Re: WARNING: at arch/x86_64/kernel/smp.c:397 smp_call_function

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Date:	Fri, 28 Sep 2007 02:34:22 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Laurent Vivier <Laurent.Vivier@...l.net>
Cc:	Fengguang Wu <wfg@...l.ustc.edu.cn>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: WARNING: at arch/x86_64/kernel/smp.c:397
 smp_call_function_mask()

On Fri, 28 Sep 2007 11:18:45 +0200 Laurent Vivier <Laurent.Vivier@...l.net> wrote:

> Andrew Morton wrote:
> > On Fri, 28 Sep 2007 10:52:08 +0200 Laurent Vivier <Laurent.Vivier@...l.net> wrote:
> >>
> >> Andi, is this correct ?
> >> Andrew, should I send a patch implementing this change ?
> > 
> > umm, I think all the smp_call_function fucntions are deadlocky if called
> > with local interrupts disabled, regardless of whether the calling CPU is in
> > the mask.
> > 
> > If CPU A is sending a cross-cpu call to CPU B and CPU B is sending a
> > cross-cpu call to CPU A, and they both have local interrupts disabled...
> 
> OK, so there are two errors:
> 
> 1- one I introduce myself (without any help from anyone) where
> smp_call_function() calls all online CPUs instead of calling all CPUs except itself.

I'd be pretty surprised if one was able to write a bug like that.  You mean
the CPU sends an IPI to itself and then loops around until it has serviced
that IPI?  And this works?  Wow.

And on_each_cpu() can call the handler function twice?

hm

> 2- one in global_flush_tlb() which calls smp_call_function() with irqs disabled.

That would be a big bug, and surely we would already have picked it up.

<looks>

argh, mainline's x86_64 smp_call_function() doesn't do the check.  We've
had *heaps* of bugs in i386 where people were running smp_call_foo() under
local_irq_disable().  I wonder how many there are in x86_64?

> I think I should at least correct #1 ?

I think we should correct all bugs ;)
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