linux-kernel - Re: [PATCH] arm64: Implement 1-,2- byte smp_load_acquire and smp_store

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Date:	Mon, 20 Apr 2015 09:08:41 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: Implement 1-,2- byte smp_load_acquire and
 smp_store_release

On Mon, Apr 20, 2015 at 06:45:53PM +0300, Andrey Ryabinin wrote:
> commit 47933ad41a86 ("arch: Introduce smp_load_acquire(), smp_store_release()")
> allowed only 4- and 8-byte smp_load_acquire, smp_store_release.
> So 1- and 2-byte cases weren't implemented in arm64.
> Later commit 536fa402221f ("compiler: Allow 1- and 2-byte smp_load_acquire()
> 				and smp_store_release()")
> allowed to use 1 and 2 byte smp_load_acquire and smp_store_release
> by adjusting the definition of __native_word().
> However, 1-,2- byte cases in arm64 version left unimplemented.
> 
> Commit 8053871d0f7f ("smp: Fix smp_call_function_single_async() locking")
> started to use smp_load_acquire() to load 2-bytes csd->flags.
> That crashes arm64 kernel during the boot.
> 
> Implement 1,2 byte cases in arm64's  smp_load_acquire()
> and smp_store_release() to fix this.
> 
> Signed-off-by: Andrey Ryabinin <a.ryabinin@...sung.com>

I am introducing a similar smp_load_acquire() case in rcutorture to
replace use of explicit memory barriers, so thank you!  ;-)

Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

> ---
>  arch/arm64/include/asm/barrier.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> index a5abb00..71f19c4 100644
> --- a/arch/arm64/include/asm/barrier.h
> +++ b/arch/arm64/include/asm/barrier.h
> @@ -65,6 +65,14 @@ do {									\
>  do {									\
>  	compiletime_assert_atomic_type(*p);				\
>  	switch (sizeof(*p)) {						\
> +	case 1:								\
> +		asm volatile ("stlrb %w1, %0"				\
> +				: "=Q" (*p) : "r" (v) : "memory");	\
> +		break;							\
> +	case 2:								\
> +		asm volatile ("stlrh %w1, %0"				\
> +				: "=Q" (*p) : "r" (v) : "memory");	\
> +		break;							\
>  	case 4:								\
>  		asm volatile ("stlr %w1, %0"				\
>  				: "=Q" (*p) : "r" (v) : "memory");	\
> @@ -81,6 +89,14 @@ do {									\
>  	typeof(*p) ___p1;						\
>  	compiletime_assert_atomic_type(*p);				\
>  	switch (sizeof(*p)) {						\
> +	case 1:								\
> +		asm volatile ("ldarb %w0, %1"				\
> +			: "=r" (___p1) : "Q" (*p) : "memory");		\
> +		break;							\
> +	case 2:								\
> +		asm volatile ("ldarh %w0, %1"				\
> +			: "=r" (___p1) : "Q" (*p) : "memory");		\
> +		break;							\
>  	case 4:								\
>  		asm volatile ("ldar %w0, %1"				\
>  			: "=r" (___p1) : "Q" (*p) : "memory");		\
> -- 
> 2.3.5
> 

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