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SubjectRe: [PATCH] workqueue: Don't double assign worker->sleeping
On 2020-04-01 11:44:06 [+0800], Lai Jiangshan wrote:
> On Wed, Apr 1, 2020 at 11:22 AM Lai Jiangshan <jiangshanlai@gmail.com> wrote:
> >
> > Hello
Hi Lai,


> > 2) wq_worker_running() can be interrupted(async-page-faulted in virtual machine)
> > and nr_running would be decreased twice.
>
> would be *increased* twice
>
> I just saw the V2 patch, this issue is not listed, but need to be fixed too.

| void wq_worker_running(struct task_struct *task)
| {
| struct worker *worker = kthread_data(task);
|
| if (!worker->sleeping)
| return;
| if (!(worker->flags & WORKER_NOT_RUNNING))
| atomic_inc(&worker->pool->nr_running);
*0
| worker->sleeping = 0;
*1
| }

So an interrupt
- before *0, the preempting caller drop early in wq_worker_sleeping(), only one
atomic_inc()

- after *1, the preempting task will invoke wq_worker_sleeping() and do
dec() + inc().

What did I miss here?

Sebastian

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