linux-kernel - Re: [PATCH 3/3] clocksource: fix can not set tsc as clocksource bug

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Date:	Fri, 05 Jul 2013 14:44:24 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	hpa@...ux.intel.com, tim.c.chen@...ux.intel.com,
	linux-kernel@...r.kernel.org, andi.kleen@...el.com,
	a.p.zijlstra@...llo.nl, mingo@...e.hu
Subject: Re: [PATCH 3/3] clocksource: fix can not set tsc as clocksource bug

On 07/05/2013 01:41 PM, Thomas Gleixner wrote:
>>>>> > >> > Unlikely, but if we have 3 watched clocksources which have the HRES
>>>>> > >> > bit set, you'd call 3 times clocksource_select().
>>> > > Also the reselect must be called outside the watchdog_lock region.
>> > 
>> > Sorry for stupid, the watchdog_lock used protect watchdog related
>> > resource. but clocksource_select doesn't touch them. So, I know it isn't
>> > necessary to put reselect under this lock. Just don't know why the
>> > reselect *must* be called outside of it?
>   clocksource_select()
>     timekeeping_notify()
>       stop_machine()
>         get_online_cpus()
> 	  might_sleep()
> 	  mutex_lock()
> 
> So we need to be in preemptible context when we call clocksource_select().

understand! many thanks!

-- 
Thanks
    Alex
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