Commit 5fe0a562 authored Apr 11, 2018 by Paul E. McKenney

rcu: Make rcu_gp_kthread() check for early-boot activity

The rcu_gp_kthread() function immediately sleeps waiting to be notified
of the need for a new grace period, which currently works because there
are a number of code sequences that will provide the needed wakeup later.
However, some of these code sequences need to acquire the root rcu_node
structure's ->lock, and contention on that lock has started manifesting.
This commit therefore makes rcu_gp_kthread() check for early-boot activity
when it starts up, omitting the initial sleep in that case.

Reported-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>

parent c91a8675

kernel/rcu/tree.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -2192,6 +2192,12 @@ static int __noreturn rcu_gp_kthread(void *arg)
		struct rcu_state *rsp = arg;
		struct rcu_node *rnp = rcu_get_root(rsp);

		/* Check for early-boot work. */
		raw_spin_lock_irq_rcu_node(rnp);
		if (need_any_future_gp(rnp))
		WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
		raw_spin_unlock_irq_rcu_node(rnp);

		rcu_bind_gp_kthread();
		for (;;) {

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