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Date: Tue, 10 Jan 2017 11:57:59 +0000
From: "Reshetova, Elena" <elena.reshetova@...el.com>
To: Kees Cook <keescook@...omium.org>
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.

I don't think it picked up this one, don't know why. All prerequisites should be in place. 
Is there a way to point it to the repo? We have everything in refcount_t branch here:
https://github.com/ereshetova/linux-stable/tree/refcount_t
Just note: the last lustre commit is there just for future work, I won't include it in testing since we gave up on trying to get it in shape. It is *way* too messy... 

>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...)

It was fully buildable at last on x86 and arm (not arm64 as was noted) and was based on linux-next/stable branch. 
I can also rebase it to 4.10-rc2 if needed. Should be trivial. 
Should we in general keep it on stable and not on linux-next? Certainly easier to test... 

Best Regards,
Elena

-Kees

--
Kees Cook
Nexus Security

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