Re: WARNING: at arch/x86_64/kernel/smp.c:397smp_call_function_mask()

From: Andrew Morton
Date: Fri Sep 28 2007 - 05:35:23 EST

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

> Andrew Morton wrote:
> > On Fri, 28 Sep 2007 10:52:08 +0200 Laurent Vivier <Laurent.Vivier@xxxxxxxx> 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?


> 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.


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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