linux-kernel - Re: migration thread and active_load

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Date:	Mon, 21 Apr 2008 22:39:34 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Dan Upton" <upton.dan.linux@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: migration thread and active_load_balance

On 21/04/2008, Dan Upton <upton.dan.linux@...il.com> wrote:
> On Mon, Apr 21, 2008 at 7:03 AM, Dmitry Adamushko
>
> <dmitry.adamushko@...il.com> wrote:
>
> > On 21/04/2008, Dan Upton <upton.dan.linux@...il.com> wrote:
>  >  > [ ... ]
>  >
>  > >
>  >  >  kernel BUG at kernel/sched.c:2103
>  >
>  >  and what's this line in your patched sched.c?
>  >
>  >  is it -- BUG_ON(!irqs_disabled());  ?
>  >
>  >  anything in your unposted code (e.g. find_coolest_cpu()) that might
>  >  re-enable the interrupts before __migration_task() is called?
>  >
>  >  If you post your modifications as a patch
>  >  (Documentation/applying-patches.txt) that contains _all_ relevant
>  >  modifications, it'd be easier to guess what's wrong.
>
>
> Yes, that's the line.  I don't recall ever reenabling interrupts,

migration_thread() -> find_coolest_cpu() -> get_temperature() ->
rdmsr_on_cpu() -> [ if your configuration is SMP ] ->
smp_call_function_single() ->

(arch/x86/kernel/smpcommon.c)
...
        if (cpu == me) {
                local_irq_disable();
                func(info);
                local_irq_enable();   <----------- REENABLES the interrupts
                put_cpu();
                return 0;
        }
...

as a result, __migrate_task() -> double_rq_lock() -> BUG_ON(!irqs_disabled())
gives you an "oops".


>
>  -dan
>

-- 
Best regards,
Dmitry Adamushko
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