blk-cgroup: factor out a helper to read rwstat counter [Linux 5.3]

This Linux kernel change "blk-cgroup: factor out a helper to read rwstat counter" is included in the Linux 5.3 release. This change is authored by Christoph Hellwig <hch [at] lst.de> on Thu Jun 6 12:26:19 2019 +0200. The commit for this change in Linux stable tree is 239eeb0 (patch).

blk-cgroup: factor out a helper to read rwstat counter

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

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

There are 12 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 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 4407972..0778e52 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -745,7 +745,7 @@ 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);

@@ -762,8 +762,7 @@ 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 76c6131..06236f5 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 *,

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