From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751039AbdAODqT (ORCPT ); Sat, 14 Jan 2017 22:46:19 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50690 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750894AbdAODor (ORCPT ); Sat, 14 Jan 2017 22:44:47 -0500 Date: Sat, 14 Jan 2017 11:54:17 -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 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170114093550.GB14970@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 17011503-0016-0000-0000-000005DFB4E9 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006435; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000199; SDB=6.00807711; UDB=6.00393283; IPR=6.00585066; BA=6.00005056; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013923; XFM=3.00000011; UTC=2017-01-15 03:44:45 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17011503-0017-0000-0000-0000368083E8 Message-Id: <20170114195417.GW5238@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-01-15_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1612050000 definitions=main-1701150056 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 14, 2017 at 10:35:50AM +0100, Ingo Molnar wrote: > > * Paul E. McKenney wrote: > > > If a process invokes synchronize_srcu(), is delayed just the right amount > > of time, and thus does not sleep when waiting for the grace period to > > complete, there is no ordering between the end of the grace period and > > the code following the synchronize_srcu(). Similarly, there can be a > > lack of ordering between the end of the SRCU grace period and callback > > invocation. > > > > This commit adds the necessary ordering. > > > > Reported-by: Lance Roy > > Signed-off-by: Paul E. McKenney > > --- > > include/linux/rcupdate.h | 12 ++++++++++++ > > kernel/rcu/srcu.c | 5 +++++ > > kernel/rcu/tree.h | 12 ------------ > > 3 files changed, 17 insertions(+), 12 deletions(-) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 01f71e1d2e94..608d56f908f2 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -1161,5 +1161,17 @@ do { \ > > ftrace_dump(oops_dump_mode); \ > > } while (0) > > > > +/* > > + * Place this after a lock-acquisition primitive to guarantee that > > + * an UNLOCK+LOCK pair act as a full barrier. This guarantee applies > > + * if the UNLOCK and LOCK are executed by the same CPU or if the > > + * UNLOCK and LOCK operate on the same lock variable. > > minor typo: > > s/an UNLOCK+LOCK pair act as > an UNLOCK+LOCK pair acts as Fixed. > > + */ > > +#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? Thanx, Paul