linux-kernel - Re: Oops in microcode sysfs registration,

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Message-ID: <b647ffbd0807311255w375a90a8v8fa4b05c81f3785f@mail.gmail.com>
Date:	Thu, 31 Jul 2008 21:55:11 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Alistair John Strachan" <alistair@...zero.co.uk>,
	"Pekka Paalanen" <pq@....fi>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	shaohua.li@...el.com, tigran@...azian.fsnet.co.uk,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Max Krasnyansky" <maxk@...lcomm.com>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Subject: Re: Oops in microcode sysfs registration,

2008/7/31 Dmitry Adamushko <dmitry.adamushko@...il.com>:
>>
>> could you please send this patch with a changelog, explanation, etc.?
>
> Now having thought a bit more on that issue, I tend to think that this
> patch is not all that nice (so I agree with Max here).
>
> The root problem is the way set_cpus_allowed_ptr() is used in
> microcode's cpu-hotplug handler. With cpu_active_map in place
> set_cpus_allowed_ptr() can't migrate a task on the soon-to-be-online
> cpu from withing a CPU_ONLINE handler (more in details here:
> http://lkml.org/lkml/2008/7/24/260)
>
> Basically, this patch marks a 'cpu' available for other tasks to be
> migrated to it before sending CPU_ONLINE notification to
> subscribers... [ now, there can be CPU_ONLINE
> http://lkml.org/lkml/2008/7/24/260handlers that has something to do
> with enabling migration/load-balancing. e.g. migration_call() ,
> although it has the highest prio and is supposed to run first in a
> chain ]
>
> In another thread, I've asked whether doing 'microcode update' in
> start_secondary() (or even at the beginning of idle_cpu() would be
> better):
>
> pros:
> - it's done as early as possible (no other tasks has started running
> on a cpu yet);
> - no actions in cpu-hotplug;
>
> cons:
> - microcode sub-systems becomes visible outside of microcode.c _but_
> it's arch-specific part anyway + with object-oriented re-work (which
> is in -tip), I think it'd be that bad.

it was supposed to be "it'd be _not_ that bad"


-- 
Best regards,
Dmitry Adamushko
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