linux-kernel - Re: [PATCH v2 01/11] counters: Introduce counter

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Message-ID: <202010071329.90E96DC2@keescook>
Date:   Wed, 7 Oct 2020 13:30:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     corbet@....net, gregkh@...uxfoundation.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/11] counters: Introduce counter_atomic* counters

On Wed, Oct 07, 2020 at 01:26:53PM -0600, Shuah Khan wrote:
> On 10/7/20 12:11 PM, Kees Cook wrote:
> > My instinct is to say leave it "int" and adjust documentation, which is
> > the least disruptive, but I am enticed by the desire to make sure a
> > counter doesn't "misbehave" and go negative when the usage wants it
> > always positive.
> > 
> 
> I would recommend leaving it as "int". Changing the API to unsigned has
> other ramifications and cascading changes.
> 
> My quick search shows me there are 612 atomic_inc_return usages and
> 14 out of them are forcing the return type from int to u32.
> 
> For atomic_read the numbers are 51 out of 5833 forcing u32. We have
> couple of options:
> 
> 1. Update the documentation since we have more cases where
>    int is just fine.
> 2. Add counter_atomic32_inc_return_u32() variant to cover these few
>    cases that are forcing the return.
> 
> I recommend going with option 1 with Documentation update and add
> option 2 when we convert one of these 60+.

Agreed: 1 seems best, and then later 2 if it feels justified. :)

-- 
Kees Cook