linux-kernel - Re: [PATCH v4 1/3] kernel.h: disable type-checks in container

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Message-Id: <20181121192507.5199cf95fd2da9573a18ca80@linux-foundation.org>
Date:   Wed, 21 Nov 2018 19:25:07 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Josh Triplett <josh@...htriplett.org>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-kernel@...r.kernel.org, NeilBrown <neilb@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>, Crt Mori <cmo@...exis.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH v4 1/3] kernel.h: disable type-checks in container_of()
 for Sparse

On Thu, 22 Nov 2018 12:14:20 +0900 Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:

> When I tried to enable BUILD_BUG_ON for Sparse, the kbuild test robot
> reported lots of "unknown expression" warnings from container_of(),
> which seemed false positive.
> 
> I addressed this in [1], but fixing Sparse is the right thing to do.
> 
> The issue was fixed by Sparse commit 0eb8175d3e9c ("fix expansion of
> function designator"), but it will take time until the fixed version
> of Sparse is widely available.
> 
> Disable the container_of() type checks for Sparse for now.
> 
> [1] https://lore.kernel.org/lkml/1542623503-3755-1-git-send-email-yamada.masahiro@socionext.com/
> 
> ...
>
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -985,6 +985,21 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
>  #define __CONCAT(a, b) a ## b
>  #define CONCATENATE(a, b) __CONCAT(a, b)
>  
> +/*
> + * TODO:
> + * Sparse emits "unknown expression" warnings.
> + * It was fixed by commit 0eb8175d3e9c0d20354763d07ce3d4c0e543d988 in Sparse.
> + * Remove the following workaround when the fixed Sparse is widely available.
> + */
> +#ifdef __CHECKER__
> +#define TYPE_CHECK_CONTAINER_OF(ptr, type, member)	do {} while (0)
> +#else
> +#define TYPE_CHECK_CONTAINER_OF(ptr, type, member) \
> +	BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) &&	\
> +			 !__same_type(*(ptr), void),			\
> +			 "pointer type mismatch in container_of()")
> +#endif

I think that's OK.  A few years hence, someone will happen upon this
comment and will perform the obvious cleanup.