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Groups > linux.kernel > #1640691
| From | "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [RFC][PATCH 1/5] tracing: Make sure RCU is watching before calling a stack trace |
| Date | 2017-05-12 21:00 +0200 |
| Message-ID | <tGnXb-lv-7@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> |
| Organization | linux.* mail to news gateway |
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
__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
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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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