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Subject: Re: [PATCH] overflow: Add __must_check attribute to check_*() helpers
To:     Matthew Wilcox <willy@infradead.org>,
        Kees Cook <keescook@chromium.org>
Cc:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Leon Romanovsky <leon@kernel.org>,
        linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com
References: <202008121450.405E4A3@keescook>
 <20200813112327.GF17456@casper.infradead.org>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <3e498585-f22f-25b8-9385-feadd55fdc7b@rasmusvillemoes.dk>
Date:   Thu, 13 Aug 2020 13:33:05 +0200
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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