----- On Apr 7, 2017, at 1:26 PM, rostedt [email protected] wrote:
> On Fri, 7 Apr 2017 17:19:05 +0000 (UTC)
> Mathieu Desnoyers <[email protected]> wrote:
>
[...]
>> > ---
>> > include/linux/tracepoint.h | 2 ++
>> > 1 file changed, 2 insertions(+)
>> >
>> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
>> > index f72fcfe..8baef96 100644
>> > --- a/include/linux/tracepoint.h
>> > +++ b/include/linux/tracepoint.h
>> > @@ -159,6 +159,8 @@ extern void syscall_unregfunc(void);
>> > TP_PROTO(data_proto), \
>> > TP_ARGS(data_args), \
>> > TP_CONDITION(cond), \
>> > + if (WARN_ON_ONCE(rcu_irq_enter_disabled())) \
>> > + return; \
>>
>> I must admit that it's a bit odd to have:
>>
>> if (WARN_ON_ONCE(rcu_irq_enter_disabled()))
>> return;
>> rcu_irq_enter_irqson()
>
> Welcome to MACRO MAGIC!
>
>>
>> as one argument to the __DO_TRACE() macro. To me it's a bit unexpected
>> coding-style wise. Am I the only one not comfortable with the proposed
>> syntax ?
>
> The entire TRACE_EVENT()/__DO_TRACE() is special.
>
> I thought about add yet another parameter, but as it doesn't change
> much, I figured this was good enough. We could beak it up if you like:
>
> #define RCU_IRQ_ENTER_CHECK \
> if (WARN_ON_ONCE(rcu_irq_enter_disabled()) \
> return; \
> rcu_irq_enter_irqson();
>
> [..]
> __DO_TRACE(&__tracepoint_##name, \
> TP_PROTO(data_proto), \
> TP_ARGS(data_args), \
> TP_CONDITION(cond), \
> PARAMS(RCU_IRQ_ENTER_CHECK), \
> rcu_irq_exit_irqson()); \
>
>
> Would that make you feel more comfortable?
No, it's almost worse and adds still adds a return that apply within
__DO_TRACE(),
but which is passed as an argument (code as macro argument), which I find really
unsettling.
I would prefer to add a new argument to __DO_TRACE, which we can call
"checkrcu", e.g.:
#define __DO_TRACE(tp, proto, args, cond, checkrcu, prercu, postrcu) \
do { \
struct tracepoint_func *it_func_ptr; \
void *it_func; \
void *__data; \
\
if (!((cond) && (checkrcu))) \
return; \
prercu; \
rcu_read_lock_sched_notrace(); \
it_func_ptr = rcu_dereference_sched((tp)->funcs); \
if (it_func_ptr) { \
do { \
it_func = (it_func_ptr)->func; \
__data = (it_func_ptr)->data; \
((void(*)(proto))(it_func))(args); \
} while ((++it_func_ptr)->func); \
} \
rcu_read_unlock_sched_notrace(); \
postrcu; \
} while (0)
And use it like this:
#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), \
!WARN_ON_ONCE(rcu_irq_enter_disabled()),\
rcu_irq_enter_irqson(), \
rcu_irq_exit_irqson()); \
}
This way we only pass evaluated expression (not code with "return" that
changes the flow) as arguments to __DO_TRACE, which makes it behave more
like a "sub-function", which is what we usually expect.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
