Commit a0ef9ec2 authored Jul 09, 2018 by Paul E. McKenney

rcu: Provide improved interrupt-from-idle check in rcu_check_callbacks()

The patch making need_resched() respond to urgent RCU-QS needs used
is_idle_task(current) to detect an interrupt from idle, which does work
reasonably, but is (in theory at least) vulnerable to loops containing
need_resched() invoked from within RCU_NONIDLE() or its tracepoint
equivalent. This commit therefore moves rcu_is_cpu_rrupt_from_idle()
to a place from which rcu_check_callbacks() can invoke it and replaces
the is_idle_task(current) with rcu_is_cpu_rrupt_from_idle().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 92aa39e9

kernel/rcu/tree.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -2474,7 +2474,7 @@ void rcu_check_callbacks(int user)
		/* The load-acquire pairs with the store-release setting to true. */
		if (smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
		/* Idle and userspace execution already are quiescent states. */
		if (!is_idle_task(current) && !user) {
		if (!rcu_is_cpu_rrupt_from_idle() && !user) {
		set_tsk_need_resched(current);
		set_preempt_need_resched();
		}

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