linux-kernel - Re: [PATCH] x86 microcode: revert some work_on

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Date:	Wed, 15 Apr 2009 14:14:07 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Peter Oruba <peter.oruba@....com>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86 microcode: revert some work_on_cpu

On Wed, 15 Apr 2009 03:55:42 am Hugh Dickins wrote:
> Revert part of af5c820a3169e81af869c113e18ec7588836cd50
> x86: cpumask: use work_on_cpu in arch/x86/kernel/microcode_core.c
> 
> That change is causing only one Intel CPU's microcode to be updated e.g.
> microcode: CPU3 updated from revision 0x9 to 0x17, date = 2005-04-22 
> where before it announced that also for CPU0 and CPU1 and CPU2.
> 
> We cannot use work_on_cpu() in the CONFIG_MICROCODE_OLD_INTERFACE code,
> because Intel's request_microcode_user() involves a copy_from_user() from
> /sbin/microcode_ctl, which therefore needs to be on that CPU at the time.

Erk.  Ack the reversion, but this needs to be fixed properly.

We can't just mug a process's affinity.  I'll look at this code again and
see what I can do.

> May be not the only problem with that commit: I've seen lockdep
> warnings from s2ram when suspending; but I think there have been other
> work_on_cpu() lockdep issues, and you may already be on to them?

Yep.

Thanks,
Rusty.
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