Re: [PATCH 1/2] reimplement flush_workqueue()

[Srivatsa Vaddagiri <vatsa@in.ibm.com>]

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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