On 01/06, Srivatsa Vaddagiri wrote:
>
> On Sat, Jan 06, 2007 at 06:10:36PM +0300, Oleg Nesterov wrote:
> > Increment hotplug_sequence earlier, under CPU_DOWN_PREPARE. We can't
> > miss the event, the task running flush_workqueue() will be re-scheduled
> > at least once before CPU actually disappears from cpu_online_map.
>
> Eww ..what happens if flush_workqueue() starts after CPU_DOWN_PREPARE?
^^^^^
Stupid me. Thanks.
> CPU_DOWN_PREPARE(8)
> hotplug_sequence++ = 10
>
> flush_workqueue()
> sequence = 10
> flush cpus 1 ....7
>
> CPU_DEAD(8)
> take_over_work(8->1)
>
> return not flushing dead cpu8 (=BUG)
I'll try to do something else tomorrow. Do you see a simple soulution?
The current usage of workqueue_mutex (I mean stable kernel) is broken
and deadlockable. We really need to change it.
Oleg.
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