linux-kernel - Re: [PATCH 2/2] x86, ACPI: Fix the wrong assignment when Handle apic/x2apic entries

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Date:	Thu, 11 Aug 2016 10:46:52 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Baoquan He <bhe@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH 2/2] x86, ACPI: Fix the wrong assignment when Handle
 apic/x2apic entries


* Baoquan He <bhe@...hat.com> wrote:

> On 08/10/16 at 02:53pm, Ingo Molnar wrote:
> > 
> > * Baoquan He <bhe@...hat.com> wrote:
> > 
> > > It won't impact the result, we still should fix the code bug.
> > > 
> > > Signed-off-by: Baoquan He <bhe@...hat.com>
> > > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > > Cc: Len Brown <len.brown@...el.com>
> > > Cc: Pavel Machek <pavel@....cz>
> > > Cc: Thomas Gleixner <tglx@...utronix.de>
> > > Cc: Ingo Molnar <mingo@...hat.com>
> > > Cc: "H. Peter Anvin" <hpa@...or.com>
> > > Cc: x86@...nel.org
> > > Cc: linux-pm@...r.kernel.org
> > > ---
> > >  arch/x86/kernel/acpi/boot.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> > > index 90d84c3..2b25d3f 100644
> > > --- a/arch/x86/kernel/acpi/boot.c
> > > +++ b/arch/x86/kernel/acpi/boot.c
> > > @@ -1031,8 +1031,8 @@ static int __init acpi_parse_madt_lapic_entries(void)
> > >  			return ret;
> > >  		}
> > >  
> > > -		x2count = madt_proc[0].count;
> > > -		count = madt_proc[1].count;
> > > +		count = madt_proc[0].count;
> > > +		x2count = madt_proc[1].count;
> > >  	}
> > >  	if (!count && !x2count) {
>           ~~~~~~~~~~~~~~~~~~~~~
> I mean here the value checking won't be impacted by the wrong
> assignment.

Indeed!

Mind putting that into the changelog? Something like:

"By pure accident the bug makes no functional difference, because the only 
 expression where we are using these values is (!count && !x2count), in which
 the variables are interchangeable, but it makes sense to fix the bug 
 nevertheless."

Thanks,

	Ingo