linux-kernel - Re: [GIT PULL] scheduler changes for v4.3

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Message-ID: <20150901084444.GB421@x4>
Date:	Tue, 1 Sep 2015 10:44:44 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>
Subject: Re: [GIT PULL] scheduler changes for v4.3

On 2015.09.01 at 10:38 +0200, Ingo Molnar wrote:
> 
> * Markus Trippelsdorf <markus@...ppelsdorf.de> wrote:
> 
> > Well, git show a1d8561172f369ba56d636df49a6b4d6d77e2123 :
> > 
> > commit a1d8561172f369ba56d636df49a6b4d6d77e2123
> > Merge: 3959df1dfb95 ff277d4250fe
> > Author: Linus Torvalds <torvalds@...ux-foundation.org>
> > Date:   Mon Aug 31 20:26:22 2015 -0700
> 
> > diff --cc kernel/cpu.c
> > index 3c91a3fdfce5,664ce5299334..82cf9dff4295
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@@ -394,15 -392,10 +394,15 @@@ static int _cpu_down(unsigned int cpu, 
> >   	smpboot_park_threads(cpu);
> >   
> >   	/*
> >  -	 * So now all preempt/rcu users must observe !cpu_active().
> >  +	 * Prevent irq alloc/free while the dying cpu reorganizes the
> >  +	 * interrupt affinities.
> >   	 */
> >  +	irq_lock_sparse();
> >   
> >  +	/*
> >  +	 * So now all preempt/rcu users must observe !cpu_active().
> >  +	 */
> > - 	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> > + 	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> >   	if (err) {
> >   		/* CPU didn't die: tell everyone.  Can't complain. */
> >   		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> 
> So the irq_lock_sparse() change is from a commit that got merged in the last merge 
> window, which is part of v4.2:
> 
>   ce0d3c0a6fb1 ("genirq: Revert sparse irq locking around __cpu_up() and move it to x86 for now")
> 
> Could you please post the patch against Linus's latest that you have tested on 
> your system to make it boot fine?
> 
> The one you posted cannot possibly build, because access to __stop_machine() is 
> gone from cpu.c:

As I wrote in my other reply. The boot failure is nondeterministic (boot
succeeds roughly every sixth time). So the bisection and the patch is
just bogus (,but the boot failure is real).

Sorry.

-- 
Markus
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