linux-kernel - Re: [PATCH -rcu] kcsan: Turn barrier instrumentation into macros

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Date:   Sat, 4 Dec 2021 07:12:37 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH -rcu] kcsan: Turn barrier instrumentation into macros

On Sat, Dec 04, 2021 at 01:57:03PM +0100, Marco Elver wrote:
> Some architectures use barriers in 'extern inline' functions, from which
> we should not refer to static inline functions.
> 
> For example, building Alpha with gcc and W=1 shows:
> 
> ./include/asm-generic/barrier.h:70:30: warning: 'kcsan_rmb' is static but used in inline function 'pmd_offset' which is not static
>    70 | #define smp_rmb()       do { kcsan_rmb(); __smp_rmb(); } while (0)
>       |                              ^~~~~~~~~
> ./arch/alpha/include/asm/pgtable.h:293:9: note: in expansion of macro 'smp_rmb'
>   293 |         smp_rmb(); /* see above */
>       |         ^~~~~~~
> 
> Which seems to warn about 6.7.4#3 of the C standard:
>   "An inline definition of a function with external linkage shall not
>    contain a definition of a modifiable object with static or thread
>    storage duration, and shall not contain a reference to an identifier
>    with internal linkage."
> 
> Fix it by turning barrier instrumentation into macros, which matches
> definitions in <asm/barrier.h>.
> 
> Perhaps we can revert this change in future, when there are no more
> 'extern inline' users left.
> 
> Link: https://lkml.kernel.org/r/202112041334.X44uWZXf-lkp@intel.com
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Marco Elver <elver@...gle.com>

Queued and pushed, thank you!

							Thanx, Paul

> ---
>  include/linux/kcsan-checks.h | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h
> index 9d2c869167f2..92f3843d9ebb 100644
> --- a/include/linux/kcsan-checks.h
> +++ b/include/linux/kcsan-checks.h
> @@ -241,28 +241,30 @@ static inline void __kcsan_disable_current(void) { }
>   * disabled with the __no_kcsan function attribute.
>   *
>   * Also see definition of __tsan_atomic_signal_fence() in kernel/kcsan/core.c.
> + *
> + * These are all macros, like <asm/barrier.h>, since some architectures use them
> + * in non-static inline functions.
>   */
>  #define __KCSAN_BARRIER_TO_SIGNAL_FENCE(name)					\
> -	static __always_inline void kcsan_##name(void)				\
> -	{									\
> +	do {									\
>  		barrier();							\
>  		__atomic_signal_fence(__KCSAN_BARRIER_TO_SIGNAL_FENCE_##name);	\
>  		barrier();							\
> -	}
> -__KCSAN_BARRIER_TO_SIGNAL_FENCE(mb)
> -__KCSAN_BARRIER_TO_SIGNAL_FENCE(wmb)
> -__KCSAN_BARRIER_TO_SIGNAL_FENCE(rmb)
> -__KCSAN_BARRIER_TO_SIGNAL_FENCE(release)
> +	} while (0)
> +#define kcsan_mb()	__KCSAN_BARRIER_TO_SIGNAL_FENCE(mb)
> +#define kcsan_wmb()	__KCSAN_BARRIER_TO_SIGNAL_FENCE(wmb)
> +#define kcsan_rmb()	__KCSAN_BARRIER_TO_SIGNAL_FENCE(rmb)
> +#define kcsan_release()	__KCSAN_BARRIER_TO_SIGNAL_FENCE(release)
>  #elif defined(CONFIG_KCSAN_WEAK_MEMORY) && defined(__KCSAN_INSTRUMENT_BARRIERS__)
>  #define kcsan_mb	__kcsan_mb
>  #define kcsan_wmb	__kcsan_wmb
>  #define kcsan_rmb	__kcsan_rmb
>  #define kcsan_release	__kcsan_release
>  #else /* CONFIG_KCSAN_WEAK_MEMORY && ... */
> -static inline void kcsan_mb(void)		{ }
> -static inline void kcsan_wmb(void)		{ }
> -static inline void kcsan_rmb(void)		{ }
> -static inline void kcsan_release(void)		{ }
> +#define kcsan_mb()	do { } while (0)
> +#define kcsan_wmb()	do { } while (0)
> +#define kcsan_rmb()	do { } while (0)
> +#define kcsan_release()	do { } while (0)
>  #endif /* CONFIG_KCSAN_WEAK_MEMORY && ... */
>  
>  /**
> -- 
> 2.34.1.400.ga245620fadb-goog
>