Messages in this thread | | | Date | Mon, 10 Apr 2017 11:29:01 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 7/7 v3] tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events |
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On Mon, Apr 10, 2017 at 02:10:12PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> > > Stack tracing discovered that there's a small location inside the RCU > infrastructure where calling rcu_irq_enter() does not work. As trace events > use rcu_irq_enter() it must make sure that it is functionable. A check > against rcu_irq_enter_disabled() is added with a WARN_ON_ONCE() as no trace > event should ever be used in that part of RCU. If the warning is triggered, > then the trace event is ignored. > > Restructure the __DO_TRACE() a bit to get rid of the prercu and postrcu, > and just have an rcucheck that does the work from within the _DO_TRACE() > macro. gcc optimization will compile out the rcucheck=0 case. > > Link: http://lkml.kernel.org/r/20170405093207.404f8deb@gandalf.local.home > > Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
As an aside, it looks like the rcu_irq_enter_disabled() settings in the RCU idle-entry code could be placed under CONFIG_PROVE_RCU=y should my idle-entry-overhead concerns prove to be well-founded. The errors would be caught during testing, but no production-side overhead.
Again, I am not necessarily agitating for this change now, just getting this possibility on the record. ;-)
Thanx, Paul
> --- > include/linux/tracepoint.h | 19 +++++++++++-------- > 1 file changed, 11 insertions(+), 8 deletions(-) > > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > index f72fcfe0e66a..cc48cb2ce209 100644 > --- a/include/linux/tracepoint.h > +++ b/include/linux/tracepoint.h > @@ -128,7 +128,7 @@ extern void syscall_unregfunc(void); > * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just > * "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto". > */ > -#define __DO_TRACE(tp, proto, args, cond, prercu, postrcu) \ > +#define __DO_TRACE(tp, proto, args, cond, rcucheck) \ > do { \ > struct tracepoint_func *it_func_ptr; \ > void *it_func; \ > @@ -136,7 +136,11 @@ extern void syscall_unregfunc(void); > \ > if (!(cond)) \ > return; \ > - prercu; \ > + if (rcucheck) { \ > + if (WARN_ON_ONCE(rcu_irq_enter_disabled())) \ > + return; \ > + rcu_irq_enter_irqson(); \ > + } \ > rcu_read_lock_sched_notrace(); \ > it_func_ptr = rcu_dereference_sched((tp)->funcs); \ > if (it_func_ptr) { \ > @@ -147,20 +151,19 @@ extern void syscall_unregfunc(void); > } while ((++it_func_ptr)->func); \ > } \ > rcu_read_unlock_sched_notrace(); \ > - postrcu; \ > + if (rcucheck) \ > + rcu_irq_exit_irqson(); \ > } while (0) > > #ifndef MODULE > -#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \ > +#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \ > static inline void trace_##name##_rcuidle(proto) \ > { \ > if (static_key_false(&__tracepoint_##name.key)) \ > __DO_TRACE(&__tracepoint_##name, \ > TP_PROTO(data_proto), \ > TP_ARGS(data_args), \ > - TP_CONDITION(cond), \ > - rcu_irq_enter_irqson(), \ > - rcu_irq_exit_irqson()); \ > + TP_CONDITION(cond), 1); \ > } > #else > #define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) > @@ -186,7 +189,7 @@ extern void syscall_unregfunc(void); > __DO_TRACE(&__tracepoint_##name, \ > TP_PROTO(data_proto), \ > TP_ARGS(data_args), \ > - TP_CONDITION(cond),,); \ > + TP_CONDITION(cond), 0); \ > if (IS_ENABLED(CONFIG_LOCKDEP) && (cond)) { \ > rcu_read_lock_sched_notrace(); \ > rcu_dereference_sched(__tracepoint_##name.funcs);\ > -- > 2.10.2 > >
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