Re: [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for trace_*_rcuidle() trace events

From: Mathieu Desnoyers
Date: Fri Apr 07 2017 - 14:16:49 EST


----- On Apr 7, 2017, at 2:10 PM, rostedt rostedt@xxxxxxxxxxx wrote:

> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
>
> 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.
>
> Link: http://lkml.kernel.org/r/20170405093207.404f8deb@xxxxxxxxxxxxxxxxxx
>
> Cc: Mathieu (making code boring) Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
>
> Mathieu,
>
> There! Are you now satisfied?

Since you reversed the boolean logic from my proposal, perhaps
rename the "rcucheck" argument to "rcudisabled" to reflect the
logic swap ?

Other than that:

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

Thanks,

Mathieu

>
>
>
> include/linux/tracepoint.h | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index f72fcfe..7f98d50 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, prercu, postrcu) \
> do { \
> struct tracepoint_func *it_func_ptr; \
> void *it_func; \
> @@ -136,6 +136,8 @@ extern void syscall_unregfunc(void);
> \
> if (!(cond)) \
> return; \
> + if (rcucheck) \
> + return; \
> prercu; \
> rcu_read_lock_sched_notrace(); \
> it_func_ptr = rcu_dereference_sched((tp)->funcs); \
> @@ -151,7 +153,7 @@ extern void syscall_unregfunc(void);
> } 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)) \
> @@ -159,6 +161,7 @@ extern void syscall_unregfunc(void);
> 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()); \
> }
> @@ -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);\
> --
> 2.9.3

--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com