Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756993AbdDRAen (ORCPT ); Mon, 17 Apr 2017 20:34:43 -0400 Received: from relay2-d.mail.gandi.net ([217.70.183.194]:45586 "EHLO relay2-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753367AbdDRAek (ORCPT ); Mon, 17 Apr 2017 20:34:40 -0400 X-Originating-IP: 50.39.160.18 Date: Mon, 17 Apr 2017 17:34:30 -0700 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH v2 tip/core/rcu 04/39] srcu: Check for tardy grace-period activity in cleanup_srcu_struct() Message-ID: <20170418003429.wa7qvhiy3vvccbxw@x> References: <20170417234452.GB19013@linux.vnet.ibm.com> <1492472726-3841-4-git-send-email-paulmck@linux.vnet.ibm.com> <20170418003332.7ocpffvkr3okbhr7@x> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170418003332.7ocpffvkr3okbhr7@x> User-Agent: NeoMutt/20170306 (1.8.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3201 Lines: 73 On Mon, Apr 17, 2017 at 05:33:32PM -0700, Josh Triplett wrote: > On Mon, Apr 17, 2017 at 04:44:51PM -0700, Paul E. McKenney wrote: > > Users of SRCU are obliged to complete all grace-period activity before > > invoking cleanup_srcu_struct(). This means that all calls to either > > synchronize_srcu() or synchronize_srcu_expedited() must have returned, > > and all calls to call_srcu() must have returned, and the last call to > > call_srcu() must have been followed by a call to srcu_barrier(). > > Furthermore, the caller must have done something to prevent any > > further calls to synchronize_srcu(), synchronize_srcu_expedited(), > > and call_srcu(). > > > > Therefore, if there has ever been an invocation of call_srcu() on > > the srcu_struct in question, the sequence of events must be as > > follows: > > > > 1. Prevent any further calls to call_srcu(). > > 2. Wait for any pre-existing call_srcu() invocations to return. > > 3. Invoke srcu_barrier(). > > 4. It is now safe to invoke cleanup_srcu_struct(). > > > > On the other hand, if there has ever been a call to synchronize_srcu() > > or synchronize_srcu_expedited(), the sequence of events must be as > > follows: > > > > 1. Prevent any further calls to synchronize_srcu() or > > synchronize_srcu_expedited(). > > 2. Wait for any pre-existing synchronize_srcu() or > > synchronize_srcu_expedited() invocations to return. > > 3. It is now safe to invoke cleanup_srcu_struct(). > > > > If there have been calls to all both types of functions (call_srcu() > > and either of synchronize_srcu() and synchronize_srcu_expedited()), then > > the caller must do the first three steps of the call_srcu() procedure > > above and the first two steps of the synchronize_s*() procedure above, > > and only then invoke cleanup_srcu_struct(). > > This commit message clearly explains the correct sequence for the > client, but not which aspects of this the change now enforces. Some of > the steps above remain the responsibility of the caller, while the > callee now checks more of them. Could you add something at the end > explaining the change and what it enforces? More importantly, perhaps this explanation could find its way into the documentation of cleanup_srcu_struct? > > Reported-by: Paolo Bonzini > > Signed-off-by: Paul E. McKenney > > With the above change: > Reviewed-by: Josh Triplett > > > kernel/rcu/srcu.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c > > index ba41a5d04b49..6beeba7b0b67 100644 > > --- a/kernel/rcu/srcu.c > > +++ b/kernel/rcu/srcu.c > > @@ -261,6 +261,11 @@ void cleanup_srcu_struct(struct srcu_struct *sp) > > { > > if (WARN_ON(srcu_readers_active(sp))) > > return; /* Leakage unless caller handles error. */ > > + if (WARN_ON(!rcu_all_batches_empty(sp))) > > + return; /* Leakage unless caller handles error. */ > > + flush_delayed_work(&sp->work); > > + if (WARN_ON(sp->running)) > > + return; /* Caller forgot to stop doing call_srcu()? */ > > free_percpu(sp->per_cpu_ref); > > sp->per_cpu_ref = NULL; > > } > > -- > > 2.5.2 > >