locking, percpu counters: introduce separate lock classes

Impact: fix lockdep false positives

Classify percpu_counter instances similar to regular lock objects --
that is, per instantiation site.

The networking code has increased its use of percpu_counters, which
leads to false positives if they are treated as a single class.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index f2e574d..f3b1258 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -220,7 +220,7 @@
 	bdi->max_prop_frac = PROP_FRAC_BASE;
 
 	for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
-		err = percpu_counter_init_irq(&bdi->bdi_stat[i], 0);
+		err = percpu_counter_init(&bdi->bdi_stat[i], 0);
 		if (err)
 			goto err;
 	}