linux-kernel - Re: [PATCH 1/2] x86/smpboot: Check APIC ID before setting up default routing

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Date:	Thu, 18 Aug 2016 10:15:15 +0000
From:	"Wei, Jiangang" <weijg.fnst@...fujitsu.com>
To:	"mingo@...nel.org" <mingo@...nel.org>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>, "bp@...e.de" <bp@...e.de>
Subject: Re: [PATCH 1/2] x86/smpboot: Check APIC ID before setting up
 default routing

On Thu, 2016-08-18 at 11:47 +0200, Ingo Molnar wrote:
> * Wei Jiangang <weijg.fnst@...fujitsu.com> wrote:
> 
> > Check the boot APIC ID firstly,
> > and then setup the default routing of APIC looks better.
> > 
> > And move default_setup_apic_routing() close to apic_bsp_setup(),
> > which staying in step with the codes in APIC_init_uniprocessor().
> > 
> > Signed-off-by: Wei Jiangang <weijg.fnst@...fujitsu.com>
> > ---
> >  arch/x86/kernel/smpboot.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> If it's not a bug then please clearly note so in the changelog and
> explain why the change results in better code.

It's not a bug.
The combination of default_setup_apic_routing() and apic_bsp_setup() is
used to enable APIC mode. If the return of read_apic_id() is not equal
to boot_cpu_physical_apicid, it means the APIC ID of current CPU‘s local
APIC  is unexpected and enable APIC mode maybe fail. so no need to set
up the apic routing.  That's why I want to move
default_setup_apic_routing() behind checking the boot APIC ID.

Sorry for obscure commit message. I will improve it in next version.

> 
> If it's fixing a bug/misfeature then please fix the changelog to
> conform to the standard changelog style:
> 
>  - first describe the symptoms of the bug - how does a user notice? 
> 
>  - then describe how the code behaves today and how that is causing the bug
> 
>  - and then only describe how it's fixed.

Thanks for your detailed explanation. I'll keep in my mind.
> 
> Thanks,
> 
>         Ingo
> 
>