Andrew Morton wrote: > On Fri, 28 Sep 2007 11:18:45 +0200 Laurent Vivier <[EMAIL PROTECTED]> wrote: > >> Andrew Morton wrote: >>> On Fri, 28 Sep 2007 10:52:08 +0200 Laurent Vivier <[EMAIL PROTECTED]> 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.
In fact, it works because __smp_call_function_mask() makes :
cpus_and(mask, mask, allbutself);
So it removes current cpu from the mask. BTW, I don't have to modify
smp_call_function(): it is correct as it is written (except from a semantic
point of view... do we care about semantic ?).
> 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 ;)
>
We don't live in a perfect world... ;-)
Moreover, I'm not able to reproduce #2 ...
Fengguang could you send me your .config and your qemu command line parameters ?
Laurent
PS: if semantic is important, you can apply attached patch...
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"Software is hard" - Donald Knuth
0001-smp_call_function-call-function-on-all-CPUs.patch
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