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Date: Fri, 25 Jun 2010 19:58:49 +0800
Message-ID: <AANLkTimiq2K6v_OhCajiktj6HzqikMZRuc8p4PK6SPjq@mail.gmail.com>
Subject: Re: [RFC][PATCH] irq_work
From: huang ying <huang.ying.caritas@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Huang Ying <ying.huang@intel.com>, Ingo Molnar <mingo@elte.hu>,
       hpa@zytor.com,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Andi Kleen <andi@firstfloor.org>
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On Fri, Jun 25, 2010 at 5:30 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>> > You can always miss an NMI since it can always happen before the
>> > callback gets done, and allowing another enqueue before the callback is
>> > complete is asking for trouble.
>>
>> If we move entry->next = NULL before entry->func(entry), we will not
>> miss the NMI. Can you show how to miss it in this way?
>
> <NMI>
>  ...
>  irq_work_queue(&my_work, func);
>  ...
> <EOI>
> <IPI>
>  irq_work_run()
>
>  <NMI>
>    irq_work_queue(&my_work, func); <FAIL>
>  <EOI>
>
>   my_func.next = NULL;

entry->func() should follows here. You can collect all information
(maybe some data in a ring buffer) from NMI handler in entry->func().
But if you place entry->NULL after entry->func(), you will really lose
a NMI notification and the information from NMI handler.

> <EOI>

> Really not that hard. Now imagine wrapping irq_work in some state and
> you reusing the state while the function is still running..

So I suggest to use another flag to signify the function is running to
distinguish.

Best Regards,
Huang Ying
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