Re: [PATCH] fix-flush_workqueue-vs-cpu_dead-race-update

[Oleg Nesterov]

On 01/06, Srivatsa Vaddagiri wrote:
>
> On Sat, Jan 06, 2007 at 07:30:35PM +0300, Oleg Nesterov wrote:
> > Stupid me. Thanks.
> > 
> > I'll try to do something else tomorrow. Do you see a simple soulution?
> 
> Sigh ..I dont see a simple solution, unless we have something like
> lock_cpu_hotplug() ..

I suspect this can't help either.

The problem is that flush_workqueue() may be called while cpu hotplug event
in progress and CPU_DEAD waits for kthread_stop(), so we have the same dead
lock if work->func() does flush_workqueue(). This means that Andrew's change
to use preempt_disable() is good and anyway needed.

I am starting to believe we need some more intrusive changes in workquue.c.

Oleg.

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