blkcg: minor updates around blkcg_policy_data

* Rename blkcg->pd[] to blkcg->cpd[] so that cpd is consistently used
  for blkcg_policy_data.

* Make blkcg_policy->cpd_init_fn() take blkcg_policy_data instead of
  blkcg.  This makes it consistent with blkg_policy_data methods and
  to-be-added cpd alloc/free methods.

* blkcg_policy_data->blkcg and cpd_to_blkcg() added so that
  cpd_init_fn() can determine the associated blkcg from
  blkcg_policy_data.

v2: blkcg_policy_data->blkcg initializations were missing.  Added.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-cgroup.c

@@ -821,7 +821,7 @@ static void blkcg_css_free(struct cgroup_subsys_state *css)
 	mutex_unlock(&blkcg_pol_mutex);
 
 	for (i = 0; i < BLKCG_MAX_POLS; i++)
-		kfree(blkcg->pd[i]);
+		kfree(blkcg->cpd[i]);
 	kfree(blkcg);
 }
 
@@ -857,15 +857,16 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
 		if (!pol || !pol->cpd_size)
 			continue;
 
-		BUG_ON(blkcg->pd[i]);
+		BUG_ON(blkcg->cpd[i]);
 		cpd = kzalloc(pol->cpd_size, GFP_KERNEL);
 		if (!cpd) {
 			ret = ERR_PTR(-ENOMEM);
 			goto free_pd_blkcg;
 		}
-		blkcg->pd[i] = cpd;
+		blkcg->cpd[i] = cpd;
+		cpd->blkcg = blkcg;
 		cpd->plid = i;
-		pol->cpd_init_fn(blkcg);
+		pol->cpd_init_fn(cpd);
 	}
 
 	spin_lock_init(&blkcg->lock);
@@ -881,7 +882,7 @@ blkcg_css_alloc(struct cgroup_subsys_state *parent_css)
 
 free_pd_blkcg:
 	for (i--; i >= 0; i--)
-		kfree(blkcg->pd[i]);
+		kfree(blkcg->cpd[i]);
 free_blkcg:
 	kfree(blkcg);
 	mutex_unlock(&blkcg_pol_mutex);
@@ -1168,9 +1169,10 @@ int blkcg_policy_register(struct blkcg_policy *pol)
 				goto err_free_cpds;
 			}
 
-			blkcg->pd[pol->plid] = cpd;
+			blkcg->cpd[pol->plid] = cpd;
+			cpd->blkcg = blkcg;
 			cpd->plid = pol->plid;
-			pol->cpd_init_fn(blkcg);
+			pol->cpd_init_fn(cpd);
 		}
 	}
 
@@ -1186,8 +1188,8 @@ int blkcg_policy_register(struct blkcg_policy *pol)
 err_free_cpds:
 	if (pol->cpd_size) {
 		list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
-			kfree(blkcg->pd[pol->plid]);
-			blkcg->pd[pol->plid] = NULL;
+			kfree(blkcg->cpd[pol->plid]);
+			blkcg->cpd[pol->plid] = NULL;
 		}
 	}
 	blkcg_policy[pol->plid] = NULL;
@@ -1222,8 +1224,8 @@ void blkcg_policy_unregister(struct blkcg_policy *pol)
 
 	if (pol->cpd_size) {
 		list_for_each_entry(blkcg, &all_blkcgs, all_blkcgs_node) {
-			kfree(blkcg->pd[pol->plid]);
-			blkcg->pd[pol->plid] = NULL;
+			kfree(blkcg->cpd[pol->plid]);
+			blkcg->cpd[pol->plid] = NULL;
 		}
 	}
 	blkcg_policy[pol->plid] = NULL;

block/cfq-iosched.c

@@ -220,7 +220,7 @@ struct cfqg_stats {
 /* Per-cgroup data */
 struct cfq_group_data {
 	/* must be the first member */
-	struct blkcg_policy_data pd;
+	struct blkcg_policy_data cpd;
 
 	unsigned int weight;
 	unsigned int leaf_weight;
@@ -612,7 +612,7 @@ static inline struct cfq_group *pd_to_cfqg(struct blkg_policy_data *pd)
 static struct cfq_group_data
 *cpd_to_cfqgd(struct blkcg_policy_data *cpd)
 {
-	return cpd ? container_of(cpd, struct cfq_group_data, pd) : NULL;
+	return cpd ? container_of(cpd, struct cfq_group_data, cpd) : NULL;
 }
 
 static inline struct blkcg_gq *cfqg_to_blkg(struct cfq_group *cfqg)
@@ -1568,12 +1568,11 @@ static void cfqg_stats_init(struct cfqg_stats *stats)
 #endif
 }
 
-static void cfq_cpd_init(const struct blkcg *blkcg)
+static void cfq_cpd_init(struct blkcg_policy_data *cpd)
 {
-	struct cfq_group_data *cgd =
-		cpd_to_cfqgd(blkcg->pd[blkcg_policy_cfq.plid]);
+	struct cfq_group_data *cgd = cpd_to_cfqgd(cpd);
 
-	if (blkcg == &blkcg_root) {
+	if (cpd_to_blkcg(cpd) == &blkcg_root) {
 		cgd->weight = 2 * CFQ_WEIGHT_DEFAULT;
 		cgd->leaf_weight = 2 * CFQ_WEIGHT_DEFAULT;
 	} else {

include/linux/blk-cgroup.h

@@ -45,7 +45,7 @@ struct blkcg {
 	struct blkcg_gq			*blkg_hint;
 	struct hlist_head		blkg_list;
 
-	struct blkcg_policy_data	*pd[BLKCG_MAX_POLS];
+	struct blkcg_policy_data	*cpd[BLKCG_MAX_POLS];
 
 	struct list_head		all_blkcgs_node;
 #ifdef CONFIG_CGROUP_WRITEBACK
@@ -88,7 +88,8 @@ struct blkg_policy_data {
  * each policy handle per-blkcg data.
  */
 struct blkcg_policy_data {
-	/* the policy id this per-policy data belongs to */
+	/* the blkcg and policy id this per-policy data belongs to */
+	struct blkcg			*blkcg;
 	int				plid;
 };
 
@@ -123,7 +124,7 @@ struct blkcg_gq {
 	struct rcu_head			rcu_head;
 };
 
-typedef void (blkcg_pol_init_cpd_fn)(const struct blkcg *blkcg);
+typedef void (blkcg_pol_init_cpd_fn)(struct blkcg_policy_data *cpd);
 typedef struct blkg_policy_data *(blkcg_pol_alloc_pd_fn)(gfp_t gfp, int node);
 typedef void (blkcg_pol_init_pd_fn)(struct blkg_policy_data *pd);
 typedef void (blkcg_pol_online_pd_fn)(struct blkg_policy_data *pd);
@@ -243,7 +244,7 @@ static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
 static inline struct blkcg_policy_data *blkcg_to_cpd(struct blkcg *blkcg,
 						     struct blkcg_policy *pol)
 {
-	return blkcg ? blkcg->pd[pol->plid] : NULL;
+	return blkcg ? blkcg->cpd[pol->plid] : NULL;
 }
 
 /**
@@ -257,6 +258,11 @@ static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd)
 	return pd ? pd->blkg : NULL;
 }
 
+static inline struct blkcg *cpd_to_blkcg(struct blkcg_policy_data *cpd)
+{
+	return cpd ? cpd->blkcg : NULL;
+}
+
 /**
  * blkg_path - format cgroup path of blkg
  * @blkg: blkg of interest