Messages in this thread | | | Date | Thu, 18 May 2017 08:47:11 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2] tracing: Make sure RCU is watching before calling a stack trace |
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On Thu, May 18, 2017 at 09:38:09AM -0400, Steven Rostedt wrote: > > From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> > > As stack tracing now requires "rcu watching", force RCU to be watching when > recording a stack trace. > > Link: http://lkml.kernel.org/r/20170512172449.879684501@goodmis.org > > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> > --- > > 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?
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 >
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