linux-kernel - Re: linux-next: build failure after merge of the tip tree

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Message-ID: <20140116121415.GP31570@twins.programming.kicks-ass.net>
Date:	Thu, 16 Jan 2014 13:14:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org
Subject: Re: linux-next: build failure after merge of the tip tree

On Tue, Jan 14, 2014 at 04:43:43PM -0500, Mikulas Patocka wrote:
> > @@ -200,7 +201,9 @@ static void speedstep_set_state(unsigned int state)
> >  		if (retry) {
> >  			pr_debug("retry %u, previous result %u, waiting...\n",
> >  					retry, result);
> > +			local_irq_restore(flags);
> 
> ^^^ this is wrong, because the function speedstep_set_state may already be 
> called with interrupts disabled from speedstep_get_freqs. So, you need to 
> enable interrupts unconditionally, even if they were disabled at the 
> beginning of the function speedstep_set_state.
> 
> I know it's dirty to enable interrupts in a function that was called with 
> disabled interrupts, but here it must be so (you could rewrite 
> speedstep_get_freqs to not disable interrupts if you want to avoid this 
> dirtiness).

Egads; I think you had better, this is vile beyond reason.

> >  			mdelay(retry * 50);
> > +			local_irq_save(flags);
> >  		}
> >  		retry++;
> >  		__asm__ __volatile__(
> > @@ -217,6 +220,7 @@ static void speedstep_set_state(unsigned int state)
> >  
> >  	/* enable IRQs */
> >  	local_irq_restore(flags);
> > +	preempt_enable();
> >  
> >  	if (new_state == state)
> >  		pr_debug("change to %u MHz succeeded after %u tries "
> 
> You need also preempt_disable/enable in speedstep_get_freqs.

Argh I see, this is really horrid.


Anyway, its Rafael's call, its his subsystem he gets to fix it when it
explodes.

/me shudders
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