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Groups > linux.kernel > #1640722
| From | Steven Rostedt <rostedt@goodmis.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace |
| Date | 2017-05-12 22:10 +0200 |
| Message-ID | <tGp2V-1mH-5@gated-at.bofh.it> (permalink) |
| References | <tGmy5-7Uc-3@gated-at.bofh.it> <tGmy6-7Uc-35@gated-at.bofh.it> <tGnu9-7Y-9@gated-at.bofh.it> <tGnDQ-cz-17@gated-at.bofh.it> <tGnXb-lv-7@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Fri, 12 May 2017 11:50:03 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> 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" <paulmck@linux.vnet.ibm.com> wrote:
> >
> > > On Fri, May 12, 2017 at 01:15:45PM -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.
> > > >
> > > > Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> > >
> > > 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
Why?
> __ftrace_trace_stack()? Or does that just cause other problems further
> down the road? Or BUG_ON(in_nmi())?
Why?
>
> But again if it cannot happen, no problem and no need for extra code.
>
We can't call stack trace from nmi anymore? It calls rcu_read_lock()
which is why we need to make sure rcu is watching, otherwise lockdep
complains.
-- Steve
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[RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace Steven Rostedt <rostedt@goodmis.org> - 2017-05-12 19:30 +0200
Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-12 20:30 +0200
Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace Steven Rostedt <rostedt@goodmis.org> - 2017-05-12 20:40 +0200
Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-12 21:00 +0200
Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace Steven Rostedt <rostedt@goodmis.org> - 2017-05-12 22:10 +0200
Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-12 22:40 +0200
Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace Steven Rostedt <rostedt@goodmis.org> - 2017-05-17 18:50 +0200
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