[PATCH 1/6] blk-cgroup: factor out a helper to read rwstat counter

[Christoph Hellwig <hch@lst.de>]

Trying to break up the crazy statements to something readable.
Also switch to an unsigned counter as it can't ever turn negative.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-cgroup.c         | 5 ++---
 include/linux/blk-cgroup.h | 7 +++++++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index b97b479e4f64..6f79ace02be4 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -750,7 +750,7 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
 	struct blkcg_gq *pos_blkg;
 	struct cgroup_subsys_state *pos_css;
 	struct blkg_rwstat sum = { };
-	int i;
+	unsigned int i;
 
 	lockdep_assert_held(&blkg->q->queue_lock);
 
@@ -767,8 +767,7 @@ struct blkg_rwstat blkg_rwstat_recursive_sum(struct blkcg_gq *blkg,
 			rwstat = (void *)pos_blkg + off;
 
 		for (i = 0; i < BLKG_RWSTAT_NR; i++)
-			atomic64_add(atomic64_read(&rwstat->aux_cnt[i]) +
-				percpu_counter_sum_positive(&rwstat->cpu_cnt[i]),
+			atomic64_add(blkg_rwstat_read_counter(rwstat, i),
 				&sum.aux_cnt[i]);
 	}
 	rcu_read_unlock();
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 76c61318fda5..06236f56a840 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -198,6 +198,13 @@ int blkcg_activate_policy(struct request_queue *q,
 void blkcg_deactivate_policy(struct request_queue *q,
 			     const struct blkcg_policy *pol);
 
+static inline u64 blkg_rwstat_read_counter(struct blkg_rwstat *rwstat,
+		unsigned int idx)
+{
+	return atomic64_read(&rwstat->aux_cnt[idx]) +
+		percpu_counter_sum_positive(&rwstat->cpu_cnt[idx]);
+}
+
 const char *blkg_dev_name(struct blkcg_gq *blkg);
 void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
 		       u64 (*prfill)(struct seq_file *,
-- 
2.20.1