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-and-tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf)
Cc: stable@xxxxxxxxxxxxxxx
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar<mingo@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
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_);
--
2.25.1
