Messages in this thread | | | Date | Thu, 17 Apr 2014 00:21:21 +0800 | Subject | Re: [PATCH V2] workqueue: fix possible race condition when rescuer VS pwq-release | From | Lai Jiangshan <> |
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On Wed, Apr 16, 2014 at 11:23 PM, Tejun Heo <tj@kernel.org> wrote: > Hello, Lai. > > On Wed, Apr 16, 2014 at 09:25:16AM +0800, Lai Jiangshan wrote: >> 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. >> */
Hi, Tejun
OK. It is better to use get_pwq(). I will also change the above comments to:
The base ref and the possible ref from rerscuer(stopped) are never dropped on per-cpu pwqs. Directly free the pwqs and wq.
The reason I quickly dropped V1 and wrote the V2 is that I saw this comment. "The base ref" is precise after I used get_pwq() in V1.
Or to avoid to change to this comments. I can also move the following code down to the bottom of the rescuer_thread().
if (kthread_should_stop()) { __set_current_state(TASK_RUNNING); rescuer->task->flags &= ~PF_WQ_WORKER; return 0; }
(I reply this email on browser, never mind the syntax). Maybe the second choice are better.
Any think?
Thanks, Lai.
> > You can just comment "pwqs might go away at any time, pin it until > rescuer is done with it" and that's actually the better way to do it. > percpu wq's not supporting attribute changes may change in the future. > What the code path wants is pinning down the pwq no matter where it > came from. There's no point in distinguishing unbound and per-cpu > here. > >> 3) get_unbound_pwq() self document. > > Not really. If the name is get_pwq_if_unbound(), maybe. Functions > which take args and become noop depending on the argument aren't > generally good ideas. There are specific cases that they are suitable > but this is just gratuituous. > > Thanks. > > -- > tejun > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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