Messages in this thread | | | Date | Fri, 27 Apr 2007 07:26:18 +0200 | From | Jarek Poplawski <> | Subject | Re: Fw: [PATCH -mm] workqueue: debug possible endless loop in cancel_rearming_delayed_work |
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On Thu, Apr 26, 2007 at 08:34:06PM +0400, Oleg Nesterov wrote: > On 04/26, Jarek Poplawski wrote: > > > > > void cancel_rearming_delayed_work(struct delayed_work *dwork) > > > { > > > struct work_struct *work = &dwork->work; > > > struct cpu_workqueue_struct *cwq = get_wq_data(work); > > > int done; > > > > I don't understand, why you think cwq cannot be NULL here. > > sure it can, this is just a template. > > > > > > > do { > > > done = 1; > > > spin_lock_irq(&cwq->lock); > > > > > > if (!list_empty(&work->entry)) > > > list_del_init(&work->entry); > > > > BTW, isn't needs_a_good_name needles after this and after del_timer positive? > > no, we still need it. work->func() may be running on another CPU as well. > > > > > > else if (test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) > > > done = del_timer(&dwork->timer) > > > > If this runs while a work function is fired in run_workqueue, > > it sets _PENDING bit, but if the work skips rearming, we have probably > > endless loop, again. > > No, if the work skips rearming (or didn't yet), we set WORK_STRUCT_PENDING > successfully.
Sorry! Should be: "If this runs while a work function is fired in run_workqueue, it sets _PENDING bit, but if the work skips rearming, I have probably endless loop, again."
> > > It is something alike to the current > > way, with some added measures: you try to shoot a work on the run, > > while queued or timer_pending, plus the _PENDING flag set, so it seems, > > there is some risk of longer than planed looping. > > Sorry, can't understand. done == 0 means that the queueing in progress, > this work should be placed on cwq->worklist very soon, most probably > right after we drop cwq->lock.
I think, theoretically, probably, maybe, there is possible some strange case, this function gets spin_lock only when: list_empty(&work->entry) == 1 && _PENDING == 1 && del_timer(&dwork->timer) == 0.
> > > I have to look at this more, at home and, if something new, I'll write > > tomorrow. So, the good news, is you should have enough sleep this time! > > Thanks for review!
OK. Here is the review:
It looks great!!! I cannot believe, it could be so "easy"!
Regards, Jarek P.
PS: probably unusable, but for my own satisfaction:
Acked-by: Jarek Poplawski <jarkao2@o2.pl - 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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