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Date:   Sat, 2 Sep 2017 12:51:02 -0700
From:   Kees Cook <>
To:     Ingo Molnar <>
Cc:     Mike Galbraith <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        LKML <>
Subject: Re: [PATCH][DEBUG] x86/refcount: split up refcount saturation handling

On Sat, Sep 2, 2017 at 3:35 AM, Ingo Molnar <> wrote:
> * Kees Cook <> wrote:
>> In support of debugging the problems Mike Galbraith has seen with
>> x86-refcount vs gcc vs network refcounts...
>> This minimizes the differences between unchecked-refcount and x86-refcount
>> by changing the refcount_dec() failure case to not saturate. The reporting
>> of negative values is reduced to pr_warn from WARN to avoid spamming dmesg
>> (which may impact race conditions). Ratelimiting is disabled just to be
>> sure no reports are being dropped.
>> Signed-off-by: Kees Cook <>
>> ---
>>  arch/x86/mm/extable.c | 51 ++++++++++++++++++++++++++++++++++-----------------
>>  kernel/panic.c        |  2 +-
>>  2 files changed, 35 insertions(+), 18 deletions(-)
> If this patch is still useful then please include it in your next refcount series.
> Better debuggability is always welcome.

It's not: this is while it seemed like something else was happening.
The most important reporting improvement is included in the final fix


Kees Cook
Pixel Security

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