Re: [PATCH 3/6] workqueue: make cancel_rearming_delayed_workqueue() work on idle dwork

[Oleg Nesterov <oleg@tv-sign.ru>]

On 02/07, Oleg Nesterov wrote:
> 
> The following code
> 
> 	schedule_delayed_work(dw);
> 	cancel_rearming_delayed_workqueue(dw);	// OK
> 	cancel_rearming_delayed_workqueue(dw);	// HANGS!
> 
> still doesn't work.

I think we have another problem with delayed_works.

cancel_rearming_delayed_workqueue() doesn't garantee that the ->func() is not
running upon return. I don't know if it is bug or not, the comment says nothing
about that.

However, we have the callers which seem to assume the opposite, example

	net/ipv4/ipvs/ip_vs_core.c

		module_exit
		    ip_vs_cleanup
		        ip_vs_control_cleanup
		            cancel_rearming_delayed_work
		// done

This is unsafe. The module may be unloaded and the memory may be freed
while defense_work_handler() is still running/preempted.

Unless I missed something, which side should be fixed?

Oleg.

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