----- On Jan 10, 2019, at 8:08 AM, rostedt [email protected] wrote: > On Wed, 9 Jan 2019 20:38:51 -0500 (EST) > Mathieu Desnoyers <[email protected]> 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
