On Mon, Apr 10, 2017 at 02:32:40PM -0400, Steven Rostedt wrote:
> On Mon, 10 Apr 2017 11:29:01 -0700
> "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
>
> > On Mon, Apr 10, 2017 at 02:10:12PM -0400, Steven Rostedt wrote:
> > > From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
> > >
> > > Stack tracing discovered that there's a small location inside the RCU
> > > infrastructure where calling rcu_irq_enter() does not work. As trace
> > > events
> > > use rcu_irq_enter() it must make sure that it is functionable. A check
> > > against rcu_irq_enter_disabled() is added with a WARN_ON_ONCE() as no
> > > trace
> > > event should ever be used in that part of RCU. If the warning is
> > > triggered,
> > > then the trace event is ignored.
> > >
> > > Restructure the __DO_TRACE() a bit to get rid of the prercu and postrcu,
> > > and just have an rcucheck that does the work from within the _DO_TRACE()
> > > macro. gcc optimization will compile out the rcucheck=0 case.
> > >
> > > Link: http://lkml.kernel.org/r/20170405093207.404f8...@gandalf.local.home
> > >
> > > Acked-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
> > > Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
> >
> > Acked-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> >
> > As an aside, it looks like the rcu_irq_enter_disabled() settings
> > in the RCU idle-entry code could be placed under CONFIG_PROVE_RCU=y
> > should my idle-entry-overhead concerns prove to be well-founded.
> > The errors would be caught during testing, but no production-side
> > overhead.
>
> Even with the underscored __this_cpu_*() calls?
That change did not completely address my concerns, but it did make me
willing to take a wait-and-see attitude. ;-)
> > Again, I am not necessarily agitating for this change now, just getting
> > this possibility on the record. ;-)
>
> That would be easy to add :-) But we can do that at a later time.
Agreed, if it is actually needed. The usual suspects will no doubt be
quick to let us know if it is needed.
Thanx, Pau
