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

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Message-ID: <51D63413.5020809@intel.com>
Date:	Fri, 05 Jul 2013 10:48:51 +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 07/04/2013 09:04 PM, Thomas Gleixner wrote:
>>> > >  static int clocksource_watchdog_kthread(void *data)
>>> > >  {
>>> > >  	struct clocksource *cs, *tmp;
>>> > > @@ -412,11 +415,14 @@ static int clocksource_watchdog_kthread(void *data)
>>> > >  
>>> > >  	mutex_lock(&clocksource_mutex);
>>> > >  	spin_lock_irqsave(&watchdog_lock, flags);
>>> > > -	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
>>> > > +	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
>>> > >  		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
>>> > >  			list_del_init(&cs->wd_list);
>>> > >  			list_add(&cs->wd_list, &unstable);
>>> > >  		}
>>> > > +		if (cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)
>>> > > +			clocksource_select();
>> > 
>> > 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?

-- 
Thanks
    Alex
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