Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 11 Jul 2018 07:27:44 -0700
From:   "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        linux-kernel@vger.kernel.org, Boqun Feng <boqun.feng@gmail.com>,
        Byungchul Park <byungchul.park@lge.com>,
        Ingo Molnar <mingo@redhat.com>,
        Julia Cartwright <julia@ni.com>,
        linux-kselftest@vger.kernel.org,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Glexiner <tglx@linutronix.de>,
        Tom Zanussi <tom.zanussi@linux.intel.com>
Subject: Re: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use
 SRCU
Reply-To: paulmck@linux.vnet.ibm.com
References: <20180628182149.226164-1-joel@joelfernandes.org>
 <20180628182149.226164-5-joel@joelfernandes.org>
 <20180711124954.GE2476@hirez.programming.kicks-ass.net>
 <20180711090003.42596c2b@gandalf.local.home>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180711090003.42596c2b@gandalf.local.home>
User-Agent: Mutt/1.5.21 (2010-09-15)
Message-Id: <20180711142744.GN3593@linux.vnet.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Jul 11, 2018 at 09:00:03AM -0400, Steven Rostedt wrote:
> On Wed, 11 Jul 2018 14:49:54 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Thu, Jun 28, 2018 at 11:21:46AM -0700, Joel Fernandes wrote:
> > > -		it_func_ptr = rcu_dereference_sched((tp)->funcs);	\  
> > 
> > I would convert to rcu_dereference_raw() to appease sparse. The fancy
> > stuff below is pointless if you then turn off all checking.
> 
> The problem with doing this is if we use a trace event without the
> proper _idle() or whatever, we wont get a warning that it is used
> incorrectly with lockdep. Or does lockdep still check if "rcu is
> watching" with rcu_dereference_raw()?

No lockdep checking is done by rcu_dereference_raw().

							Thanx, Paul

> -- Steve
> 
> > 
> > > +									\
> > > +		/*							\
> > > +		 * For rcuidle callers, use srcu since sched-rcu	\
> > > +		 * doesn't work from the idle path.			\
> > > +		 */							\
> > > +		if (rcuidle) {						\
> > > +			if (in_nmi()) {					\
> > > +				WARN_ON_ONCE(1);			\
> > > +				return; /* no srcu from nmi */		\
> > > +			}						\
> > > +									\
> > > +			idx = srcu_read_lock_notrace(&tracepoint_srcu);	\
> > > +			it_func_ptr =					\
> > > +				srcu_dereference_notrace((tp)->funcs,	\
> > > +						&tracepoint_srcu);	\
> > > +			/* To keep it consistent with !rcuidle path */	\
> > > +			preempt_disable_notrace();			\
> > > +		} else {						\
> > > +			rcu_read_lock_sched_notrace();			\
> > > +			it_func_ptr =					\
> > > +				rcu_dereference_sched((tp)->funcs);	\
> > > +		}							\  
>