[PATCH 3/3] kvfree_rcu: use migrate_disable/enable()

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

Since the page is obtained in a fully preemptible context, dropping
the lock can lead to migration onto another CPU. As a result a prev.
bnode of that CPU may be underutilised, because a decision has been
made for a CPU that was run out of free slots to store a pointer.

migrate_disable/enable() are now independent of RT, use it in order
to prevent any migration during a page request for a specific CPU it
is requested for.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 kernel/rcu/tree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 454809514c91..cad36074366d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3489,10 +3489,12 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
 			(*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
 		bnode = get_cached_bnode(*krcp);
 		if (!bnode && can_alloc) {
+			migrate_disable();
 			krc_this_cpu_unlock(*krcp, *flags);
 			bnode = (struct kvfree_rcu_bulk_data *)
 				__get_free_page(GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOMEMALLOC | __GFP_NOWARN);
 			*krcp = krc_this_cpu_lock(flags);
+			migrate_enable();
 		}
 
 		if (!bnode)
-- 
2.20.1