Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP kthread (rcuog) to be serviced.
Usually a wake up happening while running the idle task is spotted in one of the need_resched() checks carefully placed within the idle loop that can break to the scheduler.
Unfortunately in default_idle_call(), the call to rcu_idle_enter() is already beyond the last need_resched() check and we may halt the CPU with a resched request unhandled, leaving the task hanging.
Fix this with performing a last minute need_resched() check after calling rcu_idle_enter().
Reported-by: Paul E. McKenney paulmck@kernel.org Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf) Cc: stable@vger.kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Rafael J. Wysocki rafael.j.wysocki@intel.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnarmingo@kernel.org Signed-off-by: Frederic Weisbecker frederic@kernel.org --- kernel/sched/idle.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 305727ea0677..1af60dc50beb 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -109,15 +109,21 @@ void __cpuidle default_idle_call(void) rcu_idle_enter(); lockdep_hardirqs_on(_THIS_IP_);
- arch_cpu_idle(); + /* + * Last need_resched() check must come after rcu_idle_enter() + * which may wake up RCU internal tasks. + */ + if (!need_resched()) { + arch_cpu_idle(); + raw_local_irq_disable(); + }
/* - * OK, so IRQs are enabled here, but RCU needs them disabled to - * turn itself back on.. funny thing is that disabling IRQs - * will cause tracing, which needs RCU. Jump through hoops to - * make it 'work'. + * OK, so IRQs are enabled after arch_cpu_idle(), but RCU needs + * them disabled to turn itself back on.. funny thing is that + * disabling IRQs will cause tracing, which needs RCU. Jump through + * hoops to make it 'work'. */ - raw_local_irq_disable(); lockdep_hardirqs_off(_THIS_IP_); rcu_idle_exit(); lockdep_hardirqs_on(_THIS_IP_);