Commit 02e30241 authored by Neeraj Upadhyay's avatar Neeraj Upadhyay Committed by Paul E. McKenney
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rcu/nocb: Handle concurrent nocb kthreads creation 



When multiple CPUs in the same nocb gp/cb group concurrently
come online, they might try to concurrently create the same
rcuog kthread. Fix this by using nocb gp CPU's spawn mutex to
provide mutual exclusion for the rcuog kthread creation code.

[ paulmck: Whitespace fixes per kernel test robot feedback. ]

Acked-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: default avatarNeeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent a47f9f13

kernel/rcu/tree.h

+2 −0
Original line number Diff line number Diff line
@@ -203,6 +203,8 @@ struct rcu_data { 
	int nocb_defer_wakeup;		/* Defer wakeup of nocb_kthread. */

	struct timer_list nocb_timer;	/* Enforce finite deferral. */

	unsigned long nocb_gp_adv_time;	/* Last call_rcu() CB adv (jiffies). */

	struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */

					    /* spawning */



	/* The following fields are used by call_rcu, hence own cacheline. */

	raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp;

kernel/rcu/tree_nocb.h

+6 −1
Original line number Diff line number Diff line
@@ -1226,6 +1226,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) 
	raw_spin_lock_init(&rdp->nocb_gp_lock);

	timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);

	rcu_cblist_init(&rdp->nocb_bypass);

	mutex_init(&rdp->nocb_gp_kthread_mutex);

}



/*
@@ -1248,13 +1249,17 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu) 


	/* If we didn't spawn the GP kthread first, reorganize! */

	rdp_gp = rdp->nocb_gp_rdp;

	mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);

	if (!rdp_gp->nocb_gp_kthread) {

		t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,

				"rcuog/%d", rdp_gp->cpu);

		if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))

		if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) {

			mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);

			return;

		}

		WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);

	}

	mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);



	/* Spawn the kthread for this CPU. */

	t = kthread_run(rcu_nocb_cb_kthread, rdp,