linux-kernel - Re: [PATCH] fix-flush_workqueue-vs-cpu

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Message-ID: <20070106154506.GC24274@in.ibm.com>
Date:	Sat, 6 Jan 2007 21:15:06 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...l.org>, David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel@...r.kernel.org, Gautham shenoy <ego@...ibm.com>
Subject: Re: [PATCH] fix-flush_workqueue-vs-cpu_dead-race-update

On Sat, Jan 06, 2007 at 06:10:36PM +0300, Oleg Nesterov wrote:
> Increment hotplug_sequence earlier, under CPU_DOWN_PREPARE. We can't
> miss the event, the task running flush_workqueue() will be re-scheduled
> at least once before CPU actually disappears from cpu_online_map.

Eww ..what happens if flush_workqueue() starts after CPU_DOWN_PREPARE?

CPU_DOWN_PREPARE(8)
	hotplug_sequence++ = 10

					flush_workqueue()
						sequence = 10
						flush cpus 1 ....7

CPU_DEAD(8)
	take_over_work(8->1)

					return not flushing dead cpu8 (=BUG)


??
 
-- 
Regards,
vatsa
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