linux-kernel - Re: Help needed: Resume problems in 2.6.32-rc, perhaps related to preempt

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Date:	Mon, 9 Nov 2009 07:57:35 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Ingo Molnar <mingo@...e.hu>, "Rafael J. Wysocki" <rjw@...k.pl>,
	LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Greg KH <gregkh@...e.de>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: Help needed: Resume problems in 2.6.32-rc, perhaps related to
 preempt_count leakage in keventd

On Mon, 9 Nov 2009, Thomas Gleixner wrote:
> 
> I think it _IS_ releated because the worker_thread is CPU affine and
> the debug_smp_processor_id() check does:

Hmm. We do know CPU affinity is destroyed by CPU hotplug. People have 
complained about that before (for user-space processes that get moved 
around due to hot-unplug/plug).

And the suspend/resume process does CPU hotplug to take down all but one 
CPU. The workqueues should act on those events already, but maybe there's 
a bug somewhere. None of that is new to 32-rc, though - is it?

And workqueue_cpu_callback() seems buggy. It loops over the 'workqueues' 
list with no protection. Yes, we do 'stop_machine' for CPU hotplug events, 
but only for the very internal one (CPU_DYING) will the CPU notifiers be 
called with the machine stopped).

Hmm. I don't see any changes in kernel/cpu.c or kernel/workqueue.c that 
look at all relevant. But scheduler changes could certainly matter.

			Linus
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