On Tue, Dec 22, 2020 at 02:37:09AM +0100, Frederic Weisbecker wrote:
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
Tested-by: Paul E. McKenney paulmck@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();-- 2.25.1