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

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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: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-04-16 14:09:15 -07:00
parent 750d7f6a43
commit c00045be32
1 changed files with 6 additions and 5 deletions
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11
kernel/rcu/tree.c
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@ -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 ||