[046/262] mm: simplify bdi refcounting

Commit Message

Andrew Morton Nov. 5, 2021, 8:37 p.m. UTC

From: Christoph Hellwig <[e-mail]>
Subject: mm: simplify bdi refcounting

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.

[[e-mail]: add comment]
  Link: https://lkml.kernel.org/r/[e-mail]
[[e-mail]: fix typo]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Cc: Miquel Raynal <[e-mail]>
Cc: Richard Weinberger <[e-mail]>
Cc: Vignesh Raghavendra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 include/linux/backing-dev-defs.h |    3 +++
 mm/backing-dev.c                 |   13 +++++--------
 2 files changed, 8 insertions(+), 8 deletions(-)

Patch

--- a/include/linux/backing-dev-defs.h~mm-simplify-bdi-refcounting
+++ a/include/linux/backing-dev-defs.h
@@ -103,6 +103,9 @@  struct wb_completion {
  * change as blkcg is disabled and enabled higher up in the hierarchy, a wb
  * is tested for blkcg after lookup and removed from index on mismatch so
  * that a new wb for the combination can be created.
+ *
+ * Each bdi_writeback that is not embedded into the backing_dev_info must hold
+ * a reference to the parent backing_dev_info.  See cgwb_create() for details.
  */
 struct bdi_writeback {
 	struct backing_dev_info *bdi;	/* our parent bdi */
--- a/mm/backing-dev.c~mm-simplify-bdi-refcounting
+++ a/mm/backing-dev.c
@@ -291,8 +291,6 @@  static int wb_init(struct bdi_writeback
 
 	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
 
 	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 @@  out_destroy_stat:
 	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
 		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 w
 	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 w
 
 	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_de
 	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_de
 	goto out_put;
 
 err_fprop_exit:
+	bdi_put(bdi);
 	fprop_local_destroy_percpu(&wb->memcg_completions);
 err_ref_exit:
 	percpu_ref_exit(&wb->refcnt);