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Commit 5fe0a562 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarNicholas 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 (;;) {