On Tue, Oct 10, 2017 at 01:12:38AM +0000, Mathieu Desnoyers wrote: > ----- 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> Applied, thank you both! Thanx, Paul > 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 >
