linux-kernel - Re: [PATCH v3 1/6] powerpc: atomic: Make *xchg and *cmpxchg a full barrier

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Date:	Mon, 12 Oct 2015 22:23:18 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Waiman Long <waiman.long@...com>,
	Davidlohr Bueso <dave@...olabs.net>, stable@...r.kernel.org
Subject: Re: [PATCH v3 1/6] powerpc: atomic: Make *xchg and *cmpxchg a full
 barrier

Oops.. sorry. I will resend this one with correct address list.

On Mon, Oct 12, 2015 at 10:14:01PM +0800, Boqun Feng wrote:
> According to memory-barriers.txt, xchg, cmpxchg and their atomic{,64}_
> versions all need to imply a full barrier, however they are now just
> RELEASE+ACQUIRE, which is not a full barrier.
> 
> So replace PPC_RELEASE_BARRIER and PPC_ACQUIRE_BARRIER with
> PPC_ATOMIC_ENTRY_BARRIER and PPC_ATOMIC_EXIT_BARRIER in
> __{cmp,}xchg_{u32,u64} respectively to guarantee a full barrier
> semantics of atomic{,64}_{cmp,}xchg() and {cmp,}xchg().
> 
> This patch is a complement of commit b97021f85517 ("powerpc: Fix
> atomic_xxx_return barrier semantics").
> 
> Cc: stable@...r.kernel.org # 3.4.y-
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---
>  arch/powerpc/include/asm/cmpxchg.h | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h
> index ad6263c..d1a8d93 100644
> --- a/arch/powerpc/include/asm/cmpxchg.h
> +++ b/arch/powerpc/include/asm/cmpxchg.h
> @@ -18,12 +18,12 @@ __xchg_u32(volatile void *p, unsigned long val)
>  	unsigned long prev;
>  
>  	__asm__ __volatile__(
> -	PPC_RELEASE_BARRIER
> +	PPC_ATOMIC_ENTRY_BARRIER
>  "1:	lwarx	%0,0,%2 \n"
>  	PPC405_ERR77(0,%2)
>  "	stwcx.	%3,0,%2 \n\
>  	bne-	1b"
> -	PPC_ACQUIRE_BARRIER
> +	PPC_ATOMIC_EXIT_BARRIER
>  	: "=&r" (prev), "+m" (*(volatile unsigned int *)p)
>  	: "r" (p), "r" (val)
>  	: "cc", "memory");
> @@ -61,12 +61,12 @@ __xchg_u64(volatile void *p, unsigned long val)
>  	unsigned long prev;
>  
>  	__asm__ __volatile__(
> -	PPC_RELEASE_BARRIER
> +	PPC_ATOMIC_ENTRY_BARRIER
>  "1:	ldarx	%0,0,%2 \n"
>  	PPC405_ERR77(0,%2)
>  "	stdcx.	%3,0,%2 \n\
>  	bne-	1b"
> -	PPC_ACQUIRE_BARRIER
> +	PPC_ATOMIC_EXIT_BARRIER
>  	: "=&r" (prev), "+m" (*(volatile unsigned long *)p)
>  	: "r" (p), "r" (val)
>  	: "cc", "memory");
> @@ -151,14 +151,14 @@ __cmpxchg_u32(volatile unsigned int *p, unsigned long old, unsigned long new)
>  	unsigned int prev;
>  
>  	__asm__ __volatile__ (
> -	PPC_RELEASE_BARRIER
> +	PPC_ATOMIC_ENTRY_BARRIER
>  "1:	lwarx	%0,0,%2		# __cmpxchg_u32\n\
>  	cmpw	0,%0,%3\n\
>  	bne-	2f\n"
>  	PPC405_ERR77(0,%2)
>  "	stwcx.	%4,0,%2\n\
>  	bne-	1b"
> -	PPC_ACQUIRE_BARRIER
> +	PPC_ATOMIC_EXIT_BARRIER
>  	"\n\
>  2:"
>  	: "=&r" (prev), "+m" (*p)
> @@ -197,13 +197,13 @@ __cmpxchg_u64(volatile unsigned long *p, unsigned long old, unsigned long new)
>  	unsigned long prev;
>  
>  	__asm__ __volatile__ (
> -	PPC_RELEASE_BARRIER
> +	PPC_ATOMIC_ENTRY_BARRIER
>  "1:	ldarx	%0,0,%2		# __cmpxchg_u64\n\
>  	cmpd	0,%0,%3\n\
>  	bne-	2f\n\
>  	stdcx.	%4,0,%2\n\
>  	bne-	1b"
> -	PPC_ACQUIRE_BARRIER
> +	PPC_ATOMIC_EXIT_BARRIER
>  	"\n\
>  2:"
>  	: "=&r" (prev), "+m" (*p)
> -- 
> 2.5.3
> 
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