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SubjectRe: [PATCH 2/3] workqueue: not allow recursion run_workqueue
On 02/06, Lai Jiangshan wrote:
>
> Oleg Nesterov wrote:
> > On 02/05, Lai Jiangshan wrote:
> >> DEADLOCK EXAMPLE for explain my above option:
> >>
> >> (work_func0() and work_func1() are work callback, and they
> >> calls flush_workqueue())
> >>
> >> CPU#0 CPU#1
> >> run_workqueue() run_workqueue()
> >> work_func0() work_func1()
> >> flush_workqueue() flush_workqueue()
> >> flush_cpu_workqueue(0) .
> >> flush_cpu_workqueue(cpu#1) flush_cpu_workqueue(cpu#0)
> >> waiting work_func1() in cpu#1 waiting work_func0 in cpu#0
> >>
> >> DEADLOCK!
> >
> > I am not sure. Note that when work_func0() calls run_workqueue(),
> > it will clear cwq->current_work, so another flush_ on CPU#1 will
> > not wait for work_func0, no?
>
> cwq->current_work is changed only when
> !list_empty(&cwq->worklist)
> in run_workqueue().
>
> so cwq->current_work may not be changed.

Ah, indeed.

Thanks for correcting me!

Oleg.



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