On Tue, Oct 10, 2017 at 01:12:38AM +0000, Mathieu Desnoyers wrote:
> ----- On Oct 9, 2017, at 8:31 PM, rostedt rost...@goodmis.org wrote:
>
> > [ added Mathieu ]
> >
> > On Mon, 9 Oct 2017 17:22:45 -0700
> > "Paul E. McKenney" <paul...@linux.vnet.ibm.com> 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 <paul...@linux.vnet.ibm.com>
> >> Cc: Ingo Molnar <mi...@kernel.org>
> >> Cc: Steven Rostedt <rost...@goodmis.org>
> >
> > Acked-by: Steven Rostedt (VMware) <rost...@goodmis.org>
> >
>
> 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.desnoy...@efficios.com>
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
>
