----- On Jan 10, 2019, at 8:44 AM, Mathieu Desnoyers [email protected] wrote:
> ----- 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. So it ends up it happens directly on hardware on a Linux laptop. Here is the stacktrace: vmlinux!try_to_wake_up vmlinux!default_wake_function vmlinux!pollwake vmlinux!__wake_up_common vmlinux!__wake_up_common_lock vmlinux!__wake_up vmlinux!perf_event_wakeup vmlinux!perf_pending_event vmlinux!irq_work_run_list vmlinux!irq_work_run vmlinux!smp_irq_work_iterrupt vmlinux!irq_work_interrupt vmlinux!finish_task_switch vmlinux!__schedule vmlinux!schedule_idle vmlinux!do_idle vmlinux!cpu_startup_entry vmlinux!start_secondary vmlinux!secondary_startup_64 Does it raise any red flag ? Thanks, Mathieu > > 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 -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
