On Thu, 18 May 2017 11:45:28 -0700 "Paul E. McKenney" <[email protected]> wrote:
> On Thu, May 18, 2017 at 12:39:14PM -0400, Steven Rostedt wrote: > > 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 :-( > > If rcu_is_watching() returns false, yes. Of course, if rcu_is_watching() > returns true, you are golden. > Hmm, so I can just replace the entire if with: if (rcu_is_watching()) because it should be watching in NMI context, correct? -- Steve
