linux-kernel - Re: [PATCH] fix unsafe operation in high resolution timer

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Message-ID: <AANLkTimO-dACVbTtLWEPLVWwN_dgNOaEb-1JDv+8ku+_@mail.gmail.com>
Date:	Mon, 27 Dec 2010 21:12:50 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix unsafe operation in high resolution timer

On Sun, Dec 26, 2010 at 9:12 PM, Yong Zhang <yong.zhang0@...il.com> wrote:
> On Sat, Dec 25, 2010 at 10:19:11PM +0800, Hillf Danton wrote:
>> > But for a hrtimer which is not free in its callback, like a
>> > static defined one. the hrtimer could be referenced at the same
>> > time. So here you cann't just delete the two lines.
>>
>> After callback, as you agree, it is hard to determine in the current
>> implementation if the hrtimer is static defined, though another bit
>> could be added, say, in the flag word of hrtimer
>
> Yeah, that is an option, like a flag FREE_IN_CALLBACK/ONESHOT which
> indicate that. Or just let the callback return another value like

The result of callback sounds fine.
Hillf

> HRTIMER_FREED. But as I said before I'm not sure what's the best way
> to fix that. And maybe there's more suitable method.
>
> BTW, is there any user who free the hrtimer in its callback?
>
>> , so cutting the two
>> lines off is deserved.
>> And more, who will take care of the NORESTART again after callback?
>
> It's not related to NORESTART, just HRTIMER_STATE_CALLBACK.
> hrtimer'strategy somehow depends on HRTIMER_STATE_CALLBACK.
> You can take a look at the caller of hrtimer_callback_running().
>
> Thanks,
> Yong
>
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