----- On Oct 9, 2017, at 8:31 PM, rostedt rostedt@xxxxxxxxxxx wrote: > [ added Mathieu ] > > On Mon, 9 Oct 2017 17:22:45 -0700 > "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > >> The comment in tracepoint_add_func() mentions smp_read_barrier_depends(), >> whose use should be quite restricted. This commit updates the comment >> to instead mention the smp_store_release() and rcu_dereference_sched() >> that the current code actually uses. >> >> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> >> Cc: Ingo Molnar <mingo@xxxxxxxxxx> >> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> > > Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> > Yeah I think we don't need to spell out the implementation of rcu_dereference_sched() there (which actually uses lockless_dereference(), which indeed ends up relying on smp_read_barrier_depends()). The comment was a bit too low-level for the benefit of its audience. I agree with the change. Acked-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> Thanks, Mathieu > -- Steve > >> --- >> kernel/tracepoint.c | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c >> index 685c50ae6300..671b13457387 100644 >> --- a/kernel/tracepoint.c >> +++ b/kernel/tracepoint.c >> @@ -212,11 +212,10 @@ static int tracepoint_add_func(struct tracepoint *tp, >> } >> >> /* >> - * rcu_assign_pointer has a smp_wmb() which makes sure that the new >> - * probe callbacks array is consistent before setting a pointer to it. >> - * This array is referenced by __DO_TRACE from >> - * include/linux/tracepoints.h. A matching smp_read_barrier_depends() >> - * is used. >> + * rcu_assign_pointer has as smp_store_release() which makes sure >> + * that the new probe callbacks array is consistent before setting >> + * a pointer to it. This array is referenced by __DO_TRACE from >> + * include/linux/tracepoint.h using rcu_dereference_sched(). >> */ >> rcu_assign_pointer(tp->funcs, tp_funcs); > > if (!static_key_enabled(&tp->key)) -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
