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SubjectRe: [PATCH V2] workqueue: fix possible race condition when rescuer VS pwq-release
On 04/16/2014 12:47 AM, Tejun Heo wrote:
> On Fri, Mar 28, 2014 at 08:07:58PM +0800, Lai Jiangshan wrote:
>> +static inline void get_unbound_pwq(struct pool_workqueue *pwq)
>> +{
>> + if (pwq->wq->flags & WQ_UNBOUND)
>> + get_pwq(pwq);
>> +}
>> +
>> /**
>> * put_pwq - put a pool_workqueue reference
>> * @pwq: pool_workqueue to put
>> @@ -1075,6 +1081,12 @@ static void put_pwq(struct pool_workqueue *pwq)
>> schedule_work(&pwq->unbound_release_work);
>> }
>>
>> +static inline void put_unbound_pwq(struct pool_workqueue *pwq)
>> +{
>> + if (pwq->wq->flags & WQ_UNBOUND)
>> + put_pwq(pwq);
>> +}
>
> Ugh... please drop these helpers.
>
>> + get_unbound_pwq(pwq);
>
> Why not just do get_pwq() here?

V1 patch just do get_pwq().

>
> Thanks.
>

1) Our aim is to protect unbound pwq, not percpu pwq which can't be be protected by get_pwq().
2) get_pwq() will make reviewers confused/surprised, destroy_workqueue() may destroy percpu pwqs
with ref > 1. At least we need to add more comments explain this behavior. Origin comments:
/*
* The base ref is never dropped on per-cpu pwqs. Directly
* free the pwqs and wq.
*/
3) get_unbound_pwq() self document.

Thanks,
Lai


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