blk-cgroup: factor out blkcg_iostat_update()

To reduce some duplicated code, factor out blkcg_iostat_update(). No
functional change.
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220629070917.3113016-2-yanaijie@huawei.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-cgroup.c

@@ -846,6 +846,21 @@ static void blkg_iostat_sub(struct blkg_iostat *dst, struct blkg_iostat *src)
 	}
 }
 
+static void blkcg_iostat_update(struct blkcg_gq *blkg, struct blkg_iostat *cur,
+				struct blkg_iostat *last)
+{
+	struct blkg_iostat delta;
+	unsigned long flags;
+
+	/* propagate percpu delta to global */
+	flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
+	blkg_iostat_set(&delta, cur);
+	blkg_iostat_sub(&delta, last);
+	blkg_iostat_add(&blkg->iostat.cur, &delta);
+	blkg_iostat_add(last, &delta);
+	u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
+}
+
 static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
 {
 	struct blkcg *blkcg = css_to_blkcg(css);
@@ -860,8 +875,7 @@ static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
 	hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
 		struct blkcg_gq *parent = blkg->parent;
 		struct blkg_iostat_set *bisc = per_cpu_ptr(blkg->iostat_cpu, cpu);
-		struct blkg_iostat cur, delta;
-		unsigned long flags;
+		struct blkg_iostat cur;
 		unsigned int seq;
 
 		/* fetch the current per-cpu values */
@@ -870,23 +884,12 @@ static void blkcg_rstat_flush(struct cgroup_subsys_state *css, int cpu)
 			blkg_iostat_set(&cur, &bisc->cur);
 		} while (u64_stats_fetch_retry(&bisc->sync, seq));
 
-		/* propagate percpu delta to global */
-		flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
-		blkg_iostat_set(&delta, &cur);
-		blkg_iostat_sub(&delta, &bisc->last);
-		blkg_iostat_add(&blkg->iostat.cur, &delta);
-		blkg_iostat_add(&bisc->last, &delta);
-		u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
+		blkcg_iostat_update(blkg, &cur, &bisc->last);
 
 		/* propagate global delta to parent (unless that's root) */
-		if (parent && parent->parent) {
-			flags = u64_stats_update_begin_irqsave(&parent->iostat.sync);
-			blkg_iostat_set(&delta, &blkg->iostat.cur);
-			blkg_iostat_sub(&delta, &blkg->iostat.last);
-			blkg_iostat_add(&parent->iostat.cur, &delta);
-			blkg_iostat_add(&blkg->iostat.last, &delta);
-			u64_stats_update_end_irqrestore(&parent->iostat.sync, flags);
-		}
+		if (parent && parent->parent)
+			blkcg_iostat_update(parent, &blkg->iostat.cur,
+					    &blkg->iostat.last);
 	}
 
 	rcu_read_unlock();