Messages in this thread | | | Date | Thu, 10 Jan 2019 11:44:13 -0500 (EST) | From | Mathieu Desnoyers <> | Subject | Re: Possible use of RCU while in extended QS: idle vs RCU read-side in interrupt vs rcu_eqs_exit |
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----- On Jan 10, 2019, at 8:08 AM, rostedt rostedt@goodmis.org wrote:
> On Wed, 9 Jan 2019 20:38:51 -0500 (EST) > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > >> Hi Paul, >> >> I've had a user report that trace_sched_waking() appears to be >> invoked while !rcu_is_watching() in some situation, so I started >> digging into the scheduler idle code. > > I'm wondering if this isn't a bug. Do you have the backtrace for where > trace_sched_waking() was called without rcu watching?
I strongly suspect a bug as well. I'm awaiting a reproducer from the user whom reported this issue so I can add a WARN_ON_ONCE(!rcu_is_watching()) in the scheduler code near trace_sched_waking() and gather a backtrace.
It still has to be confirmed, but I suspect this have been triggered within a HyperV guest. It may therefore be related to a virtualized environment.
I'll try to ask more specifically on which environment this was encountered.
Thanks,
Mathieu
> > -- Steve > >> >> It appears that interrupts are re-enabled before rcu_eqs_exit() is >> invoked when exiting idle code from the scheduler. >> >> I wonder what happens if an interrupt handler (including scheduler code) >> happens to issue a RCU read-side critical section before rcu_eqs_exit() >> is called ? Is there some code on interrupt entry that ensures rcu eqs >> state is exited in such scenario ? >> >> Thanks, >> >> Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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