[PATCH 5/5] mm: simplify bdi refcounting

[Christoph Hellwig]

Move grabbing and releasing the bdi refcount out of the common
wb_init/wb_exit helpers into code that is only used for the non-default
memcg driven bdi_writeback structures.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 mm/backing-dev.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 768e9ae489f66..5ccb250898083 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -291,8 +291,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 
 	memset(wb, 0, sizeof(*wb));
 
-	if (wb != &bdi->wb)
-		bdi_get(bdi);
 	wb->bdi = bdi;
 	wb->last_old_flush = jiffies;
 	INIT_LIST_HEAD(&wb->b_dirty);
@@ -316,7 +314,7 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 
 	err = fprop_local_init_percpu(&wb->completions, gfp);
 	if (err)
-		goto out_put_bdi;
+		return err;
 
 	for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
 		err = percpu_counter_init(&wb->stat[i], 0, gfp);
@@ -330,9 +328,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
 	while (i--)
 		percpu_counter_destroy(&wb->stat[i]);
 	fprop_local_destroy_percpu(&wb->completions);
-out_put_bdi:
-	if (wb != &bdi->wb)
-		bdi_put(bdi);
 	return err;
 }
 
@@ -373,8 +368,6 @@ static void wb_exit(struct bdi_writeback *wb)
 		percpu_counter_destroy(&wb->stat[i]);
 
 	fprop_local_destroy_percpu(&wb->completions);
-	if (wb != &wb->bdi->wb)
-		bdi_put(wb->bdi);
 }
 
 #ifdef CONFIG_CGROUP_WRITEBACK
@@ -397,6 +390,7 @@ static void cgwb_release_workfn(struct work_struct *work)
 	struct bdi_writeback *wb = container_of(work, struct bdi_writeback,
 						release_work);
 	struct blkcg *blkcg = css_to_blkcg(wb->blkcg_css);
+	struct backing_dev_info *bdi = wb->bdi;
 
 	mutex_lock(&wb->bdi->cgwb_release_mutex);
 	wb_shutdown(wb);
@@ -416,6 +410,7 @@ static void cgwb_release_workfn(struct work_struct *work)
 
 	percpu_ref_exit(&wb->refcnt);
 	wb_exit(wb);
+	bdi_put(bdi);
 	WARN_ON_ONCE(!list_empty(&wb->b_attached));
 	kfree_rcu(wb, rcu);
 }
@@ -497,6 +492,7 @@ static int cgwb_create(struct backing_dev_info *bdi,
 	INIT_LIST_HEAD(&wb->b_attached);
 	INIT_WORK(&wb->release_work, cgwb_release_workfn);
 	set_bit(WB_registered, &wb->state);
+	bdi_get(bdi);
 
 	/*
 	 * The root wb determines the registered state of the whole bdi and
@@ -528,6 +524,7 @@ static int cgwb_create(struct backing_dev_info *bdi,
 	goto out_put;
 
 err_fprop_exit:
+	bdi_put(bdi);
 	fprop_local_destroy_percpu(&wb->memcg_completions);
 err_ref_exit:
 	percpu_ref_exit(&wb->refcnt);
-- 
2.30.2