On Thu, 18 May 2017 08:47:11 -0700 "Paul E. McKenney" <[email protected]> wrote:
> On Thu, May 18, 2017 at 09:38:09AM -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. > > > > Link: http://lkml.kernel.org/r/[email protected] > > > > Cc: "Paul E. McKenney" <[email protected]> > > Signed-off-by: Steven Rostedt (VMware) <[email protected]> > > --- > > > > Changes since v1: > > > > My testing discovered that the stack trace can be called with > > interrupts enabled, which is a no no to have when calling > > rcu_irq_enter(). When interrupts are enabled, as with being in an > > NMI, RCU will also be watching. > > > > kernel/trace/trace.c | 26 +++++++++++++++++++++++++- > > 1 file changed, 25 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > > index fcc9a2d..34a98ba 100644 > > --- a/kernel/trace/trace.c > > +++ b/kernel/trace/trace.c > > @@ -2568,7 +2568,31 @@ static inline void ftrace_trace_stack(struct > > trace_array *tr, > > void __trace_stack(struct trace_array *tr, unsigned long flags, int skip, > > int pc) > > { > > - __ftrace_trace_stack(tr->trace_buffer.buffer, flags, skip, pc, NULL); > > + struct ring_buffer *buffer = tr->trace_buffer.buffer; > > + > > + /* > > + * When an NMI triggers, RCU is enabled via rcu_nmi_enter() > > + * Also, RCU is always enabled when interrupts are. > > + */ > > + if (!irqs_disabled() || in_nmi()) { > > You lost me on this one. RCU might not be watching if irqs are > enabled, for example, in the idle loop. What am I missing here? > Hmm, no, maybe I'm missing something :-/ OK, so if we trace in the idle loop, rcu may not be watching, so I may need to byte the bullet and use the rcu_irq_enter_irqon() instead :-( -- Steve > Thanx, Paul > > > + __ftrace_trace_stack(buffer, flags, skip, pc, NULL); > > + return; > > + } > > + > > + /* > > + * It is possible that a function is being traced in a > > + * location that RCU is not watching. A call to > > + * rcu_irq_enter() will make sure that it is, but there's > > + * a few internal rcu functions that could be traced > > + * where that wont work either. In those cases, we just > > + * do nothing. > > + */ > > + if (unlikely(rcu_irq_enter_disabled())) > > + return; > > + > > + rcu_irq_enter(); > > + __ftrace_trace_stack(buffer, flags, skip, pc, NULL); > > + rcu_irq_exit(); > > } > > > > /** > > -- > > 2.9.3 > >
