[RFC PATCH v1 15/17] blk-cgroup: remove blkg radix tree preloading

[Yu Kuai <yukuai@kernel.org>]

From: Yu Kuai <yukuai@fygo.io>

blkg creation is now serialized by q->blkcg_mutex and no longer runs
under q->queue_lock.  The radix tree is initialized with GFP_NOWAIT, so
radix_tree_insert() cannot sleep while blkcg->lock is held and the old
preload dance is no longer needed.

Remove the preload calls and the associated unwind path.

Signed-off-by: Yu Kuai <yukuai@fygo.io>
---
 block/blk-cgroup.c | 22 ++--------------------
 1 file changed, 2 insertions(+), 20 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 71313bb3c4f3..b99ab8d67798 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -420,7 +420,6 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, struct gendisk *disk,
 			pol->pd_init_fn(blkg->pd[i]);
 	}
 
-	/* insert */
 	spin_lock_irq(&blkcg->lock);
 	ret = radix_tree_insert(&blkcg->blkg_tree, disk->queue->id, blkg);
 	if (likely(!ret)) {
@@ -875,16 +874,10 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 			goto fail_unlock;
 		}
 
-		if (radix_tree_preload(GFP_KERNEL)) {
-			blkg_free(new_blkg);
-			ret = -ENOMEM;
-			goto fail_unlock;
-		}
-
 		if (!blkcg_policy_enabled(q, pol)) {
 			blkg_free(new_blkg);
 			ret = -EOPNOTSUPP;
-			goto fail_preloaded;
+			goto fail_unlock;
 		}
 
 		rcu_read_lock();
@@ -896,12 +889,10 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 			blkg = blkg_create(pos, disk, new_blkg);
 			if (IS_ERR(blkg)) {
 				ret = PTR_ERR(blkg);
-				goto fail_preloaded;
+				goto fail_unlock;
 			}
 		}
 
-		radix_tree_preload_end();
-
 		if (pos == blkcg)
 			goto success;
 	}
@@ -909,8 +900,6 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 	ctx->blkg = blkg;
 	return 0;
 
-fail_preloaded:
-	radix_tree_preload_end();
 fail_unlock:
 	mutex_unlock(&q->blkcg_mutex);
 	/*
@@ -1448,7 +1437,6 @@ int blkcg_init_disk(struct gendisk *disk)
 {
 	struct request_queue *q = disk->queue;
 	struct blkcg_gq *new_blkg, *blkg;
-	bool preloaded;
 
 	/*
 	 * If the queue is shared across disk rebind (e.g., SCSI), the
@@ -1466,8 +1454,6 @@ int blkcg_init_disk(struct gendisk *disk)
 	if (!new_blkg)
 		return -ENOMEM;
 
-	preloaded = !radix_tree_preload(GFP_KERNEL);
-
 	/* Make sure the root blkg exists. */
 	mutex_lock(&q->blkcg_mutex);
 	blkg = blkg_create(&blkcg_root, disk, new_blkg);
@@ -1475,16 +1461,12 @@ int blkcg_init_disk(struct gendisk *disk)
 		goto err_unlock;
 	q->root_blkg = blkg;
 
-	if (preloaded)
-		radix_tree_preload_end();
 	mutex_unlock(&q->blkcg_mutex);
 
 	return 0;
 
 err_unlock:
 	mutex_unlock(&q->blkcg_mutex);
-	if (preloaded)
-		radix_tree_preload_end();
 	return PTR_ERR(blkg);
 }
 
-- 
2.51.0