On Fri, May 12, 2017 at 02:36:19PM -0400, Steven Rostedt wrote:
> On Fri, 12 May 2017 11:25:35 -0700
> "Paul E. McKenney" <[email protected]> wrote:
>
> > On Fri, May 12, 2017 at 01:15:45PM -0400, Steven Rostedt wrote:
> > > From: "Steven Rostedt (VMware)" <[email protected]>
> > >
> > > As stack tracing now requires "rcu watching", force RCU to be watching
> > > when
> > > recording a stack trace.
> > >
> > > Signed-off-by: Steven Rostedt (VMware) <[email protected]>
> >
> > Assuming that you never get to __trace_stack() if in an NMI handler,
> > this looks good to me!
> >
> > In contrast, if if __trace_stack() ever is called from an NMI handler,
> > invoking rcu_irq_enter() can be fatal.
>
> Then someone may die.
>
> OK, what's the case of running this in nmi? How does perf do it?
I have no idea. If it cannot happen, then it cannot happen and all
is well, RCU is happy, and I am happy. ;-)
> Do we just skip the check if it is in an nmi?
>
> if (!in_nmi()) {
> if (unlikely(rcu_irq_enter_disabled()))
> return;
> rcu_irq_enter();
> }
>
> __ftrace_trace_stack();
>
> if (!in_nmi())
> rcu_irq_exit();
>
> ?
If it -can- happen, bail out of the function without doing the
__ftrace_trace_stack()? Or does that just cause other problems further
down the road? Or BUG_ON(in_nmi())?
But again if it cannot happen, no problem and no need for extra code.
Thanx, Paul
