From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3v1Mgm3CJfzDqWJ for ; Sun, 15 Jan 2017 14:44:51 +1100 (AEDT) Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v0F3i0RB102772 for ; Sat, 14 Jan 2017 22:44:48 -0500 Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154]) by mx0b-001b2d01.pphosted.com with ESMTP id 27ynffsa0t-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Sat, 14 Jan 2017 22:44:48 -0500 Received: from localhost by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 14 Jan 2017 20:44:47 -0700 Date: Sat, 14 Jan 2017 13:41:59 -0800 From: "Paul E. McKenney" To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, will.deacon@arm.com, boqun.feng@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering Reply-To: paulmck@linux.vnet.ibm.com References: <20170114091941.GA22961@linux.vnet.ibm.com> <1484385601-23379-2-git-send-email-paulmck@linux.vnet.ibm.com> <20170114093550.GB14970@gmail.com> <20170114195417.GW5238@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20170114195417.GW5238@linux.vnet.ibm.com> Message-Id: <20170114214159.GA7098@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, Jan 14, 2017 at 11:54:17AM -0800, Paul E. McKenney wrote: > On Sat, Jan 14, 2017 at 10:35:50AM +0100, Ingo Molnar wrote: > > * Paul E. McKenney wrote: [ . . . ] > > > + */ > > > +#ifdef CONFIG_PPC > > > +#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ > > > +#else /* #ifdef CONFIG_PPC */ > > > +#define smp_mb__after_unlock_lock() do { } while (0) > > > +#endif /* #else #ifdef CONFIG_PPC */ > > > > Yeah, so I realize that this was pre-existing code, but putting CONFIG_$ARCH > > #ifdefs into generic headers is generally frowned upon. > > > > The canonical approach would be either to define a helper Kconfig variable that > > can be set by PPC (but other architectures don't need to set it), or to expose a > > suitable macro (function) for architectures to define in their barrier.h arch > > header file. > > Very well, I will add a separate commit for this. 4.11 OK? Does the patch below seem reasonable? Thanx, Paul ------------------------------------------------------------------------ commit 271c0601237c41a279f975563e13837bace0df03 Author: Paul E. McKenney Date: Sat Jan 14 13:32:50 2017 -0800 rcu: Make arch select smp_mb__after_unlock_lock() strength The definition of smp_mb__after_unlock_lock() is currently smp_mb() for CONFIG_PPC and a no-op otherwise. It would be better to instead provide an architecture-selectable Kconfig option, and select the strength of smp_mb__after_unlock_lock() based on that option. This commit therefore creates CONFIG_ARCH_WEAK_RELACQ, has PPC select it, and bases the definition of smp_mb__after_unlock_lock() on this new CONFIG_ARCH_WEAK_RELACQ Kconfig option. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney Cc: Peter Zijlstra Cc: Will Deacon Cc: Boqun Feng Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michael Ellerman Cc: diff --git a/arch/Kconfig b/arch/Kconfig index 99839c23d453..94dd90d33f95 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -316,6 +316,9 @@ config HAVE_CMPXCHG_LOCAL config HAVE_CMPXCHG_DOUBLE bool +config ARCH_WEAK_RELACQ + bool + config ARCH_WANT_IPC_PARSE_VERSION bool diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index a8ee573fe610..e7083d27271e 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -165,6 +165,7 @@ config PPC select HAVE_ARCH_HARDENED_USERCOPY select HAVE_KERNEL_GZIP select HAVE_CC_STACKPROTECTOR + select ARCH_WEAK_RELACQ config GENERIC_CSUM def_bool CPU_LITTLE_ENDIAN diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 357b32aaea48..5fdfe874229e 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -1175,11 +1175,11 @@ do { \ * if the UNLOCK and LOCK are executed by the same CPU or if the * UNLOCK and LOCK operate on the same lock variable. */ -#ifdef CONFIG_PPC +#ifdef CONFIG_ARCH_WEAK_RELACQ #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ -#else /* #ifdef CONFIG_PPC */ +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ #define smp_mb__after_unlock_lock() do { } while (0) -#endif /* #else #ifdef CONFIG_PPC */ +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ #endif /* __LINUX_RCUPDATE_H */