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SubjectRe: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU
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()?

-- Steve

>
> > + \
> > + /* \
> > + * For rcuidle callers, use srcu since sched-rcu \
> > + * doesn't work from the idle path. \
> > + */ \
> > + if (rcuidle) { \
> > + if (in_nmi()) { \
> > + WARN_ON_ONCE(1); \
> > + return; /* no srcu from nmi */ \
> > + } \
> > + \
> > + idx = srcu_read_lock_notrace(&tracepoint_srcu); \
> > + it_func_ptr = \
> > + srcu_dereference_notrace((tp)->funcs, \
> > + &tracepoint_srcu); \
> > + /* To keep it consistent with !rcuidle path */ \
> > + preempt_disable_notrace(); \
> > + } else { \
> > + rcu_read_lock_sched_notrace(); \
> > + it_func_ptr = \
> > + rcu_dereference_sched((tp)->funcs); \
> > + } \

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