linux-kernel - Re: [PATCH 1/7] Freezer: Read PF_BORROWED

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Message-ID: <20070512010117.GB540@tv-sign.ru>
Date:	Sat, 12 May 2007 05:01:17 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH 1/7] Freezer: Read PF_BORROWED_MM in a nonracy way

On 05/12, Oleg Nesterov wrote:
> 
> Do we need freezer? Should we freeze kernel threads? I can't judge. I tried
> to read a long thread about suspend, and failed to understand it.
> 
> I personally think we can simplify things if CPU-hotplug use freezer, at least.

Just a small example,

	debug_smp_processor_id:

		/*
		 * Kernel threads bound to a single CPU can safely use
		 * smp_processor_id():
		 */
		this_mask = cpumask_of_cpu(this_cpu);

		if (cpus_equal(current->cpus_allowed, this_mask))
			goto out;

This is not true with CONFIG_HOTPLUG_CPU. This becomes true if we freeze
the kernel threads from CPU_DOWN_PREPARE to CPU_DEAD.

Oleg.

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