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

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Date:	Tue, 1 Sep 2015 10:56:27 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
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


* Markus Trippelsdorf <markus@...ppelsdorf.de> wrote:

> 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.

No problem. Please let us know if any of these commits does turn out to be the 
culprit. (Which is always a possibility.)

Thanks,

	Ingo
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