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SubjectRe: [PATCH v9 4/7] tracepoint: Make rcuidle tracepoint callers use SRCU
----- On Jul 11, 2018, at 11:17 AM, Peter Zijlstra peterz@infradead.org wrote:

> On Wed, Jul 11, 2018 at 09:06:49AM -0400, Steven Rostedt wrote:
>> On Wed, 11 Jul 2018 14:56:47 +0200
>> Peter Zijlstra <peterz@infradead.org> wrote:
>>
>> > On Thu, Jun 28, 2018 at 11:21:46AM -0700, Joel Fernandes wrote:
>> > > static inline void tracepoint_synchronize_unregister(void)
>> > > {
>> > > + synchronize_srcu(&tracepoint_srcu);
>> > > synchronize_sched();
>> > > }
>> >
>> > Given you below do call_rcu_sched() and then call_srcu(), isn't the
>> > above the wrong way around?
>>
>> Good catch!
>>
>> release_probes()
>> call_rcu_sched()
>> ---> rcu_free_old_probes() queued
>>
>> tracepoint_synchronize_unregister()
>> synchronize_srcu(&tracepoint_srcu);
>> < finishes right away >
>> synchronize_sched()
>> --> rcu_free_old_probes()
>> --> srcu_free_old_probes() queued
>>
>> Here tracepoint_synchronize_unregister() returned before the srcu
>> portion ran.
>
> I just read the comment that goes with that function; the order doesn't
> matter. All we want to ensure is that the unregistration is visible to
> either sched or srcu tracepoint users.

Exactly, the order does not matter here.

Thanks,

Mathieu


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