From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751514AbdJEJv0 (ORCPT ); Thu, 5 Oct 2017 05:51:26 -0400 Received: from merlin.infradead.org ([205.233.59.134]:58518 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298AbdJEJvZ (ORCPT ); Thu, 5 Oct 2017 05:51:25 -0400 Date: Thu, 5 Oct 2017 11:50:59 +0200 From: Peter Zijlstra 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, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com Subject: Re: [PATCH tip/core/rcu 7/9] rcu: Pretend ->boost_mtx acquired legitimately Message-ID: <20171005095059.5hm2pumwpv75gvuk@hirez.programming.kicks-ass.net> References: <20171004212915.GA10089@linux.vnet.ibm.com> <1507152575-11055-7-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: <1507152575-11055-7-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 04, 2017 at 02:29:33PM -0700, Paul E. McKenney wrote: > RCU priority boosting uses rt_mutex_init_proxy_locked() to initialize an > rt_mutex structure in locked state held by some other task. When that > other task releases it, lockdep complains (quite accurately, but a bit > uselessly) that the other task never acquired it. This complaint can > suppress other, more helpful, lockdep complaints, and in any case it is > a false positive. > > This commit therefore uses the mutex_acquire() macro to make it look > like that other process legitimately acquired the lock, thus suppressing > this lockdep false-positive complaint. > > Of course, if lockdep ever learns about rt_mutex_init_proxy_locked(), > this commit will need to be reverted. > > Signed-off-by: Paul E. McKenney This is a consequence of me doing: f5694788ad8d ("rt_mutex: Add lockdep annotations") Right? > --- > kernel/rcu/tree_plugin.h | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index fed95fa941e6..60bfb16c9a1a 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -529,8 +529,11 @@ void rcu_read_unlock_special(struct task_struct *t) > } > > /* Unboost if we were boosted. */ > - if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) > + if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) { > + /* For lockdep, pretend we acquired lock honestly. */ > + mutex_acquire(&rnp->boost_mtx.dep_map, 0, 0, _RET_IP_); > rt_mutex_unlock(&rnp->boost_mtx); > + } So I'm thinking the problem is that you're mixing rt_mutex and PI-futex primitives here. As per commit: 5293c2efda37 ("futex,rt_mutex: Provide futex specific rt_mutex API") these are two separate APIs, that should, ideally, not be mixed. The 'right' counterpart to rt_mutex_init_proxy_locked() is rt_mutex_futex_unlock() (which very much does not include lockdep bits).