Commit c00045be authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu/nocb: Make rcutree_migrate_callbacks() start at leaf rcu_node structure 



Because rcutree_migrate_callbacks() is invoked infrequently and because
an exact snapshot of the grace-period state might save some callbacks a
second trip through a grace period, this function has used the root
rcu_node structure.  However, this safe-second-trip optimization
happens only if rcutree_migrate_callbacks() races with grace-period
initialization, so it is not worth the added mental load.  This commit
therefore makes rcutree_migrate_callbacks() start with the leaf rcu_node
structures, as is done elsewhere.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 750d7f6a

kernel/rcu/tree.c

+6 −5
Original line number Diff line number Diff line
@@ -3157,8 +3157,8 @@ void rcutree_migrate_callbacks(int cpu) 
{

	unsigned long flags;

	struct rcu_data *my_rdp;

	struct rcu_node *my_rnp;

	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);

	struct rcu_node *rnp_root = rcu_get_root();

	bool needwake;



	if (rcu_segcblist_is_offloaded(&rdp->cblist) ||
@@ -3167,18 +3167,19 @@ void rcutree_migrate_callbacks(int cpu) 


	local_irq_save(flags);

	my_rdp = this_cpu_ptr(&rcu_data);

	my_rnp = my_rdp->mynode;

	if (rcu_nocb_adopt_orphan_cbs(my_rdp, rdp, flags)) {

		local_irq_restore(flags);

		return;

	}

	raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */

	raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */

	/* Leverage recent GPs and set GP for new callbacks. */

	needwake = rcu_advance_cbs(rnp_root, rdp) ||

		   rcu_advance_cbs(rnp_root, my_rdp);

	needwake = rcu_advance_cbs(my_rnp, rdp) ||

		   rcu_advance_cbs(my_rnp, my_rdp);

	rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);

	WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=

		     !rcu_segcblist_n_cbs(&my_rdp->cblist));

	raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);

	raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);

	if (needwake)

		rcu_gp_kthread_wake();

	WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||

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