linux-kernel - Re: [PATCH 6/8] PM: Add suspend blocking work.

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Message-ID: <i2vd6200be21004280002tde778c02h1586b4c06de2a89a@mail.gmail.com>
Date:	Wed, 28 Apr 2010 00:02:36 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 6/8] PM: Add suspend blocking work.

2010/4/27 Tejun Heo <tj@...nel.org>:
> Hello,
>
>> +static void suspend_blocking_work_complete(struct suspend_blocking_work *work)
>> +{
>> +     unsigned long flags;
>> +
>> +     WARN_ON(!work->active);
>> +     spin_lock_irqsave(&work->lock, flags);
>> +     if (!--work->active)
>> +             suspend_unblock(&work->suspend_blocker);
>> +     spin_unlock_irqrestore(&work->lock, flags);
>> +}
>
> Maybe work->active can be an atomic_t and the lock can be removed?
>

I need the spinlock to prevent the work from getting re-queued before
suspend_unblock.

>> +/**
>> + * suspend_blocking_work_destroy - Destroy suspend_blocking_work
>> + * @work: The work item in question
>> + *
>> + * If the work was ever queued on more then one workqueue all but the last
>> + * workqueue must be flushed before calling suspend_blocking_work_destroy.
>
> As it's calling cancel_work_sync(), the above is not true.  As long as
> no one is trying to queue it again, suspend_blocking_work_destroy() is
> safe to call regardless of how the work has been used.
>

I'm not sure what the best terminology is here, but cancel_work_sync()
only waits for work running on all the cpu-workqueues of the last
workqueue. So, if the caller queued the work on more than one
workqueue, suspend_blocking_work_destroy does not ensure that the
suspend_blocking_work structure is not still in use (it should trigger
the WARN_ON though).

>> +void suspend_blocking_work_destroy(struct suspend_blocking_work *work)
>> +{
>> +     cancel_suspend_blocking_work_sync(work);
>> +     WARN_ON(work->active);
>> +     suspend_blocker_destroy(&work->suspend_blocker);
>> +}
>> +EXPORT_SYMBOL(suspend_blocking_work_destroy);
>
> Other than the above, it looks good to me.
>
> Thanks.
>
> --
> tejun
>



-- 
Arve Hjønnevåg
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