linux-kernel - Re: [PATCH v3 01/41] lcoking/barriers, arch: Use smp barriers in smp_store

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Date:	Tue, 12 Jan 2016 08:28:44 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	virtualization@...ts.linux-foundation.org,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Joe Perches <joe@...ches.com>,
	David Miller <davem@...emloft.net>, linux-ia64@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	sparclinux@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-metag@...r.kernel.org, linux-mips@...ux-mips.org,
	x86@...nel.org, user-mode-linux-devel@...ts.sourceforge.net,
	adi-buildroot-devel@...ts.sourceforge.net,
	linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
	xen-devel@...ts.xenproject.org,
	Davidlohr Bueso <dave@...olabs.net>,
	Davidlohr Bueso <dbueso@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH v3 01/41] lcoking/barriers, arch: Use smp barriers in
 smp_store_release()

On Sun, Jan 10, 2016 at 04:16:32PM +0200, Michael S. Tsirkin wrote:
> From: Davidlohr Bueso <dave@...olabs.net>
> 
> With commit b92b8b35a2e ("locking/arch: Rename set_mb() to smp_store_mb()")
> it was made clear that the context of this call (and thus set_mb)
> is strictly for CPU ordering, as opposed to IO. As such all archs
> should use the smp variant of mb(), respecting the semantics and
> saving a mandatory barrier on UP.
> 
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: <linux-arch@...r.kernel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: dave@...olabs.net
> Link: http://lkml.kernel.org/r/1445975631-17047-3-git-send-email-dave@stgolabs.net
> Signed-off-by: Ingo Molnar <mingo@...nel.org>

Aside from a need for s/lcoking/locking/ in the subject line:

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

> ---
>  arch/ia64/include/asm/barrier.h    | 2 +-
>  arch/powerpc/include/asm/barrier.h | 2 +-
>  arch/s390/include/asm/barrier.h    | 2 +-
>  include/asm-generic/barrier.h      | 2 +-
>  4 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
> index df896a1..209c4b8 100644
> --- a/arch/ia64/include/asm/barrier.h
> +++ b/arch/ia64/include/asm/barrier.h
> @@ -77,7 +77,7 @@ do {									\
>  	___p1;								\
>  })
> 
> -#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); mb(); } while (0)
> +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
> 
>  /*
>   * The group barrier in front of the rsm & ssm are necessary to ensure
> diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> index 0eca6ef..a7af5fb 100644
> --- a/arch/powerpc/include/asm/barrier.h
> +++ b/arch/powerpc/include/asm/barrier.h
> @@ -34,7 +34,7 @@
>  #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
>  #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
> 
> -#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); mb(); } while (0)
> +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while (0)
> 
>  #ifdef __SUBARCH_HAS_LWSYNC
>  #    define SMPWMB      LWSYNC
> diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
> index d68e11e..7ffd0b1 100644
> --- a/arch/s390/include/asm/barrier.h
> +++ b/arch/s390/include/asm/barrier.h
> @@ -36,7 +36,7 @@
>  #define smp_mb__before_atomic()		smp_mb()
>  #define smp_mb__after_atomic()		smp_mb()
> 
> -#define smp_store_mb(var, value)		do { WRITE_ONCE(var, value); mb(); } while (0)
> +#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); smp_mb(); } while (0)
> 
>  #define smp_store_release(p, v)						\
>  do {									\
> diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
> index b42afad..0f45f93 100644
> --- a/include/asm-generic/barrier.h
> +++ b/include/asm-generic/barrier.h
> @@ -93,7 +93,7 @@
>  #endif	/* CONFIG_SMP */
> 
>  #ifndef smp_store_mb
> -#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); mb(); } while (0)
> +#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); smp_mb(); } while (0)
>  #endif
> 
>  #ifndef smp_mb__before_atomic
> -- 
> MST
>