linux-kernel - Re: [patch v4 1/2] stop_machine: enable __stop_machine() to be called from the cpu online path

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Message-ID: <20110613195613.GA11196@elte.hu>
Date:	Mon, 13 Jun 2011 21:56:13 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	tglx@...utronix.de, hpa@...or.com, trenn@...ell.com,
	prarit@...hat.com, tj@...nel.org, rusty@...tcorp.com.au,
	linux-kernel@...r.kernel.org, youquan.song@...el.com,
	stable@...nel.org
Subject: Re: [patch v4 1/2] stop_machine: enable __stop_machine() to be
 called from the cpu online path


* Suresh Siddha <suresh.b.siddha@...el.com> wrote:

> Currently stop machine infrastructure can be called only from a cpu that is
> online. But for !CONFIG_SMP, we do allow calling __stop_machine() before the
> cpu is online.
> 
> x86 for example requires stop machine infrastructure in the cpu online path
> and currently implements its own stop machine (using stop_one_cpu_nowait())
> for MTRR initialization in the cpu online path.
> 
> Enhance the __stop_machine() so that it can be called before the cpu
> is onlined. This will pave the way for code consolidation and address potential
> deadlocks caused by multiple mechanisms of doing system wide rendezvous.
> 
> This will also address the behavioral differences of __stop_machine()
> between SMP and UP builds.
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> Cc: stable@...nel.org    # v2.6.35+
> ---
>  include/linux/stop_machine.h |   11 +++--
>  kernel/stop_machine.c        |   91 ++++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 93 insertions(+), 9 deletions(-)

Btw., this is *way* too risky for a -stable backport.

Thanks,

	Ingo
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