linux-kernel - Re: workqueue deadlock

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Message-ID: <20061211054545.GC5339@in.ibm.com>
Date:	Mon, 11 Dec 2006 11:15:45 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Bjorn Helgaas <bjorn.helgaas@...com>,
	linux-kernel@...r.kernel.org, Myron Stowe <myron.stowe@...com>,
	Jens Axboe <axboe@...nel.dk>, Dipankar <dipankar@...ibm.com>,
	Gautham shenoy <ego@...ibm.com>
Subject: Re: workqueue deadlock

On Sun, Dec 10, 2006 at 04:16:00AM -0800, Andrew Morton wrote:
> One quite different way of addressing all of this is to stop using
> stop_machine_run() for hotplug synchronisation and switch to the swsusp
> freezer infrastructure: all kernel threads and user processes need to stop
> and park themselves in a known state before we allow the CPU to be removed.
> lock_cpu_hotplug() becomes a no-op.

Well ...you still need to provide some mechanism for stable access to
cpu_online_map in blocking functions (ex: do_event_scan_all_cpus). 
Freezing-tasks/Resuming-them-after-hotp-unplug is definitely not one of them 
(when they resume, online_map would have changed under their feet).

> Dunno if it'll work - I only just thought of it.  It sure would simplify
> things.

-- 
Regards,
vatsa
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