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

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Date:	Tue, 1 Sep 2015 09:27:41 +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 2015.08.31 at 19:24 +0200, Ingo Molnar wrote:
> > Please pull the latest sched-core-for-linus git tree from:
> > 
> >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus
> > 
> >    # HEAD: ff277d4250fe715b6666219b1a3423b863418794 sched/deadline: Fix comment in enqueue_task_dl()
> 
> Linus,
> 
> your merge (commit a1d8561172f369ba) breaks booting on my machine.

So I just double checked Linus's merge resolution, re-created it from scratch, and 
it looks correct. Furthermore, I resolved the conflict similarly in the past and 
this resolution had been in -tip and linux-next testing for some while.

But I noticed something weird in your revert patch:

> 
> I wrote down the backtrace:
> 
> map_vsyscall
> kvm_arch_hardware_setup
> map_vsyscall
> kvm_init
> map_vsyscall
> do_one_initcall
> kernel_init_freeable
> rest_init
> kernel_init
> ret_from_fork
> rest_init
> 
> RIP: svm_hardware_setup
> 
> Reverting your merge resolution fixes the issue:
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 82cf9dff4295..873aa0757b04 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -397,12 +397,11 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  	 * Prevent irq alloc/free while the dying cpu reorganizes the
>  	 * interrupt affinities.
>  	 */
> -	irq_lock_sparse();

So where does this chunk come from? None of the trees nor the merge resolution 
touches this code.

Maybe you had other changes in your tree that interfered?

That missing irq_lock_sparse() might indeed break the boot. But that's not 
something that got in there from Linus's tree AFAICS.

>  	/*
>  	 * 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);

This change cannot possibly have built on Linus's tree, as __stop_machine() got 
unexported, it is now internal and static to kernel/stop_machine.c...

So could you please double check your side?

Thanks,

	Ingo
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