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Date: Thu, 5 Jan 2017 11:33:56 -0800
From: Kees Cook <keescook@...omium.org>
To: "Reshetova, Elena" <elena.reshetova@...el.com>
Cc: AKASHI Takahiro <takahiro.akashi@...aro.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "arnd@...db.de" <arnd@...db.de>, 
	"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com" <mingo@...hat.com>, 
	"Anvin, H Peter" <h.peter.anvin@...el.com>, "peterz@...radead.org" <peterz@...radead.org>, 
	"will.deacon@....com" <will.deacon@....com>, "dwindsor@...il.com" <dwindsor@...il.com>, 
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, "ishkamiel@...il.com" <ishkamiel@...il.com>
Subject: Re: [RFC PATCH 08/19] kernel, mm: convert from
 atomic_t to refcount_t

On Thu, Jan 5, 2017 at 1:56 AM, Reshetova, Elena
<elena.reshetova@...el.com> wrote:
>> On Thu, Dec 29, 2016 at 08:56:00AM +0200, Elena Reshetova wrote:
>> > refcount_t type and corresponding API should be
>> > used instead of atomic_t when the variable is used as
>> > a reference counter. Convert the cases found.
>> > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
>> > index 7dd14e8..1d59aca 100644
>> > --- a/arch/arm/kernel/smp.c
>> > +++ b/arch/arm/kernel/smp.c
>> > @@ -371,7 +371,7 @@ asmlinkage void secondary_start_kernel(void)
>> >      * reference and switch to it.
>> >      */
>> >     cpu = smp_processor_id();
>> > -   atomic_inc(&mm->mm_count);
>> > +   refcount_inc(&mm->mm_count);
>> >     current->active_mm = mm;
>> >     cpumask_set_cpu(cpu, mm_cpumask(mm));
>> >
>>
>> If this is the case, arm64 has almost the same code.
>
> Thank you! I haven't tried to build on arm64 this yet (as well as on other arches). I am pretty sure there are more cases on other arches that are missed.
> That's why I was hoping that we can run this series to the automatic build infra.
>
> @Kees, how did you do it before for previous patches? Who should be contacted to get a build-test on all arches?

Normally the 0day builder should pick it up from the mailing list, but
if it doesn't (and it may not due to the missing prerequisite
patches), I can create a branch on kernel.org and it will pick it up
there.

Are you able to build a series that includes refcount_t implementation
(so there is a single series that contains all the prerequisites), and
base it on v4.10-rc2? That should give 0day no problems in doing a
merge and test (since -next mutates every day...)

-Kees

-- 
Kees Cook
Nexus Security

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