From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751802AbdANJf7 (ORCPT ); Sat, 14 Jan 2017 04:35:59 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35724 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751640AbdANJfz (ORCPT ); Sat, 14 Jan 2017 04:35:55 -0500 Date: Sat, 14 Jan 2017 10:35:50 +0100 From: Ingo Molnar To: "Paul E. McKenney" 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 Message-ID: <20170114093550.GB14970@gmail.com> References: <20170114091941.GA22961@linux.vnet.ibm.com> <1484385601-23379-2-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1484385601-23379-2-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * 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 > + */ > +#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. Thanks, Ingo