linux-kernel - Re: [patch 3/5] [PATCH 3/5] x86: Run Intel ucode-updates via workqueue.

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Date:	Wed, 6 Aug 2008 17:56:20 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Arjan van de Ven" <arjan@...radead.org>
Cc:	"Peter Oruba" <peter.oruba@....com>, "Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Max Krasnyansky" <maxk@...lcomm.com>,
	"Tigran Aivazian" <tigran@...azian.fsnet.co.uk>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 3/5] [PATCH 3/5] x86: Run Intel ucode-updates via workqueue.

2008/8/6 Arjan van de Ven <arjan@...radead.org>:
> On Wed, 6 Aug 2008 17:21:20 +0200
> Peter Oruba <peter.oruba@....com> wrote:
>
> [ no description or reason ]
>
> Why is this?

More details are available here.

I've also suggested to do ucode-updates as early as possible  from
start_secondary() (or whatever low-level code).

The second patch (do via workqueue) was just a proof-of-concept (to
show that it does fix a crash).

>
> I'm not very happy about this.. it means practically that this stuff
> *has* to run late. Probably later than we want to.

Currently, it runs from cpu-hotplug-notifier(CPU_ONLINE, ...)
[ and crashes with .26+ due to a reason you may find via the
aforementioned link ] - by this moment, at least kernel threads may
running on this cpu -- so it's not that early.

> (Like.. we may want to redo the microcode during resume.. which is
> not a schedulable context)

I'm not sure what's "schedulable context" here terms but the existing
code makes use of set_cpus_allowed_ptr() which means a caller expects
to be able to be migrated onto a target cpu and do ucode-update while
running on it.

Moreover, the way set_cpus_allowed_ptr() is used there seems to be
race wrt. sched_setaffinity().

-- 
Best regards,
Dmitry Adamushko
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