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Date: Sun, 26 Dec 2010 21:12:05 +0800
From: Yong Zhang <yong.zhang0@gmail.com>
To: Hillf Danton <dhillf@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fix unsafe operation in high resolution timer
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Reply-To: Yong Zhang <yong.zhang0@gmail.com>
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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
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