linux-kernel - Re: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop

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Date:	Tue, 11 Nov 2008 16:11:51 +0100
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Vegard Nossum" <vegard.nossum@...il.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Rafael J. Wysocki" <rjw@...k.pl>,
	"Heiko Carstens" <heiko.carstens@...ibm.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Kernel Testers List" <kernel-testers@...r.kernel.org>,
	"Rusty Russell" <rusty@...tcorp.com.au>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Oleg Nesterov" <oleg@...hat.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop_machine

2008/11/11 Vegard Nossum <vegard.nossum@...il.com>:
> On Tue, Nov 11, 2008 at 11:52 AM, Ingo Molnar <mingo@...e.hu> wrote:
>> [ Cc:-ed workqueue/locking/suspend-race-condition experts. ]
>>
>> Seems like the new kernel/stop_machine.c logic has a race for the test
>> sequence above. (Below is the bisected commit again, maybe the race is
>> visible via email review as well.)
>
> I try again.
>
> I think that the test for stop_machine_data in stop_cpu() should not
> have been moved from __stop_machine().

Do you mean the following test?

        if (!active_cpus) {
                if (cpu == first_cpu(cpu_online_map))
                        smdata = &active;
        } else {
                if (cpu_isset(cpu, *active_cpus))
                        smdata = &active;
        }

> Because now cpu_online_map may
> change in-between calls to stop_cpu() (if the callback tries to
> online/offline CPUs), and the end result may be different.

take_cpu_down() may not run earlier than stop_cpu() on all the cpus
have completed the STOPMACHINE_DISABLE_IRQ step, iow. "state ==
STOPMACHINE_RUN". By that moment, 'smdata' has been set up on all
cpus... if this is the case you had in mind.


>
> Maybe?
>
>
> Vegard
>


-- 
Best regards,
Dmitry Adamushko
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