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

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Message-ID: <20070107144236.GB149@tv-sign.ru>
Date:	Sun, 7 Jan 2007 17:42:36 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
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 01/07, Oleg Nesterov wrote:
> 
> How about:
> 
> 	CPU_DEAD does nothing. After __cpu_disable() cwq->thread runs on
> 	all CPUs and becomes idle when it flushes cwq->worklist: nobody
> 	will add work_struct on that list.

Also, we can add cpu_workqueue_struct->should_exit_after_flush flag, but
we have to be careful to serialize with destroy_workqueue/CPU_UP.

> 	CPU_UP:
> 		if (!cwq->thread)
> 			create_workqueue_thread();
> 		else
> 			set_cpus_allowed(newcpu);
> 
> 	flush_workqueue:
> 		for_each_possible_cpu()		// NOT online!
> 			if (cwq->thread)
> 				flush_cpu_workqueue()

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