linux-kernel - Re: [PATCH 1/2] reimplement flush

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Date:	Tue, 9 Jan 2007 10:31:04 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>,
	David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Gautham R Shenoy <ego@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] reimplement flush_workqueue()

On Fri, Dec 29, 2006 at 08:18:27PM +0300, Oleg Nesterov wrote:
> Remove ->remove_sequence, ->insert_sequence, and ->work_done from struct
> cpu_workqueue_struct. To implement flush_workqueue() we can queue a barrier
> work on each CPU and wait for its completition.

Oleg,
	Because of this change, was curious to know if this is possible:


CPU0					CPU1
(Thread0)

flush_workqueue()
					queue_work(W1)	
  flush_cpu_workqueue(cpu1)
    insert_barrier(B1)
      wait_on_completion();
	
					run_workqueue()
					   W1.func();
					     flush_workqueue();
						B1.func(); <- wakes Thread0

The intention of barrier B1 was to wait untill W1 was -complete-. If
W1.func()->....->something() were to call flush_workqueue on the same
workqueue, then we would be returning from the barrier prematurely.

Looks possible in theory. Don't know if it is a practical issue.

-- 
Regards,
vatsa
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