From: Joel Fernandes <joel@joelfernandes.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.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
Date: Wed, 11 Jul 2018 13:52:49 -0700 [thread overview]
Message-ID: <20180711205249.GA32091@joelaf.mtv.corp.google.com> (raw)
In-Reply-To: <20180711104618.05dc4b46@gandalf.local.home>
On Wed, Jul 11, 2018 at 10:46:18AM -0400, Steven Rostedt wrote:
> On Wed, 11 Jul 2018 07:27:44 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > 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().
>
> Correct, but I think we can do this regardless. So Joel please resend
> with Peter's suggestion.
>
> The reason being is because of this:
>
>
> #define __DECLARE_TRACE(name, proto, args, cond, data_proto, data_args) \
> extern struct tracepoint __tracepoint_##name; \
> static inline void trace_##name(proto) \
> { \
> if (static_key_false(&__tracepoint_##name.key)) \
> __DO_TRACE(&__tracepoint_##name, \
> TP_PROTO(data_proto), \
> TP_ARGS(data_args), \
> TP_CONDITION(cond), 0); \
> if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \
> rcu_read_lock_sched_notrace(); \
> rcu_dereference_sched(__tracepoint_##name.funcs);\
> rcu_read_unlock_sched_notrace(); \
> } \
> }
>
> Because lockdep would only trigger warnings when the tracepoint was
> enabled and used in a place it shouldn't be, we added the above
> IS_ENABLED(CONFIG_LOCKDEP) part to test regardless if the the
> tracepoint was enabled or not. Because we do this, we don't need to
> have the test in the __DO_TRACE() code itself. That means we can clean
> up the code as per Peter's suggestion.
Sounds good, I'm Ok with making this change.
Just to clarify, are you proposing to change the rcu_dereference_sched to
rcu_dereference_raw in both __DECLARE_TRACE and __DO_TRACE?
thanks!
- Joel
next prev parent reply other threads:[~2018-07-11 20:52 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-28 18:21 [PATCH v9 0/7] Centralize and unify usage of preempt/irq tracepoints Joel Fernandes
2018-06-28 18:21 ` [PATCH v9 1/7] srcu: Add notrace variants of srcu_read_{lock,unlock} Joel Fernandes
2018-06-28 18:21 ` [PATCH v9 2/7] srcu: Add notrace variant of srcu_dereference Joel Fernandes
2018-06-28 18:21 ` [PATCH v9 3/7] trace/irqsoff: Split reset into separate functions Joel Fernandes
2018-06-28 18:21 ` [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU Joel Fernandes
2018-07-11 12:49 ` Peter Zijlstra
2018-07-11 13:00 ` Steven Rostedt
2018-07-11 14:27 ` Paul E. McKenney
2018-07-11 14:46 ` Steven Rostedt
2018-07-11 15:15 ` Paul E. McKenney
2018-07-11 20:56 ` Joel Fernandes
2018-07-12 1:22 ` Steven Rostedt
2018-07-12 2:35 ` Joel Fernandes
2018-07-11 20:52 ` Joel Fernandes [this message]
2018-07-12 3:21 ` Steven Rostedt
2018-07-12 4:28 ` Joel Fernandes
2018-07-12 13:35 ` Steven Rostedt
2018-07-12 19:17 ` Joel Fernandes
2018-07-12 20:15 ` Steven Rostedt
2018-07-12 20:29 ` Joel Fernandes
2018-07-12 20:31 ` Steven Rostedt
2018-07-11 12:53 ` Peter Zijlstra
2018-07-12 2:32 ` Joel Fernandes
2018-07-11 12:56 ` Peter Zijlstra
2018-07-11 13:06 ` Steven Rostedt
2018-07-11 15:17 ` Peter Zijlstra
2018-07-11 15:26 ` Steven Rostedt
2018-07-11 16:46 ` Mathieu Desnoyers
2018-07-11 16:40 ` Mathieu Desnoyers
2018-07-12 0:31 ` Joel Fernandes
2018-07-12 1:26 ` Steven Rostedt
2018-06-28 18:21 ` [PATCH v9 5/7] tracing: Centralize preemptirq tracepoints and unify their usage Joel Fernandes
2018-07-06 22:06 ` Steven Rostedt
2018-07-07 4:20 ` Joel Fernandes
2018-07-10 14:20 ` Steven Rostedt
2018-07-10 17:33 ` Joel Fernandes
2018-07-11 13:12 ` Peter Zijlstra
2018-07-11 13:19 ` Steven Rostedt
2018-07-11 13:22 ` Steven Rostedt
2018-07-12 8:38 ` Joel Fernandes
2018-07-12 13:37 ` Steven Rostedt
2018-07-12 0:44 ` Joel Fernandes
2018-06-28 18:21 ` [PATCH v9 6/7] lib: Add module to simulate atomic sections for testing preemptoff tracers Joel Fernandes
2018-07-11 0:47 ` Steven Rostedt
2018-07-11 5:26 ` Joel Fernandes
2018-06-28 18:21 ` [PATCH v9 7/7] kselftests: Add tests for the preemptoff and irqsoff tracers Joel Fernandes
2018-07-11 0:49 ` Steven Rostedt
2018-07-11 5:27 ` Joel Fernandes
2018-07-03 14:15 ` [PATCH v9 0/7] Centralize and unify usage of preempt/irq tracepoints Joel Fernandes
2018-07-03 14:23 ` Steven Rostedt
-- strict thread matches above, loose matches on Subject: below --
2018-06-21 22:32 Joel Fernandes
2018-06-21 22:32 ` [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU Joel Fernandes
2018-06-07 20:38 [PATCH v9 0/7] Centralize and unify usage of preempt/irq Joel Fernandes
2018-06-07 20:38 ` [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU Joel Fernandes
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