linux-kernel - Re: [PATCH] overflow: Add __must_check attribute to check

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Date:   Thu, 13 Aug 2020 13:33:05 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Matthew Wilcox <willy@...radead.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] overflow: Add __must_check attribute to check_*() helpers

On 13/08/2020 13.23, Matthew Wilcox wrote:
> On Wed, Aug 12, 2020 at 02:51:52PM -0700, Kees Cook wrote:
>> +/*
>> + * Allows to effectively us apply __must_check to a macro so we can have
>> + * both the type-agnostic benefits of the macros while also being able to
>> + * enforce that the return value is, in fact, checked.
>> + */
>> +static inline bool __must_check __must_check_bool(bool condition)
>> +{
>> +	return unlikely(condition);
>> +}
> 
> I'm fine with the concept, but this is a weirdly-generically-named
> function that has a very specific unlikely() in it.  So I'd call
> this __must_check_overflow() and then it's obvious that overflow is
> unlikely(), whereas it's not obvious that __must_check_bool() is going
> to be unlikely().

Incidentally, __must_check_overflow was what was actually Suggested-by
me - though I didn't think too hard about that name, I certainly agree
with your reasoning.

I still don't know if (un)likely annotations actually matter when used
this way, but at least the same pattern is used in kernel/sched/, so
probably.

Rasmus