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Date: Fri, 27 Apr 2018 12:13:30 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Joel Fernandes <joelaf@google.com>, linux-kernel@vger.kernel.org,
        Peter Zilstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Tom Zanussi <tom.zanussi@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Glexiner <tglx@linutronix.de>,
        Boqun Feng <boqun.feng@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Fenguang Wu <fengguang.wu@intel.com>,
        Baohong Liu <baohong.liu@intel.com>,
        Vedang Patel <vedang.patel@intel.com>, kernel-team@android.com
Subject: Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks
 executing with preempt on
Message-ID: <20180427121330.40b7ef15@gandalf.local.home>
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References: <20180427042656.190746-1-joelaf@google.com>
        <20180427155701.GL26088@linux.vnet.ibm.com>
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On Fri, 27 Apr 2018 08:57:01 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> > +		if (preempt_on) {					\
> > +			WARN_ON_ONCE(in_nmi()); /* no srcu from nmi */	\  
> 
> Very good on this check, thank you!

I think you need to return and not call the read lock.

			if (WARN_ON_ONCE(in_nmi()))
				return;

> 
> > +			idx = srcu_read_lock(&tracepoint_srcu);         \  
> 
> Hmmm...  Do I need to create a _notrace variant of srcu_read_lock()
> and srcu_read_unlock()?

I think so.

-- Steve

> 
> > +			it_func_ptr = srcu_dereference((tp)->funcs,	\
> > +						&tracepoint_srcu);	\
> > +		} else {						\
> > +			rcu_read_lock_sched_notrace();			\
> > +			it_func_ptr =					\
> > +				rcu_dereference_sched((tp)->funcs);	\
> > +		}							\
> > +									\