In preparation for implementing lockless slab shrink, use new APIs to
dynamically allocate the md-bcache shrinker, so that it can be freed
asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
read-side critical section when releasing the struct cache_set.

Signed-off-by: Qi Zheng <redacted>
---
  drivers/md/bcache/bcache.h |  2 +-
  drivers/md/bcache/btree.c  | 27 ++++++++++++++++-----------
  drivers/md/bcache/sysfs.c  |  3 ++-
  3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 5a79bb3c272f..c622bc50f81b 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h

@@ -541,7 +541,7 @@ struct cache_set {
  	struct bio_set		bio_split;
  
  	/* For the btree cache */
-	struct shrinker		shrink;
+	struct shrinker		*shrink;
  
  	/* For the btree cache and anything allocation related */
  	struct mutex		bucket_lock;

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index fd121a61f17c..c176c7fc77d9 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c

@@ -667,7 +667,7 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush)
  static unsigned long bch_mca_scan(struct shrinker *shrink,
  				  struct shrink_control *sc)
  {
-	struct cache_set *c = container_of(shrink, struct cache_set, shrink);
+	struct cache_set *c = shrink->private_data;
  	struct btree *b, *t;
  	unsigned long i, nr = sc->nr_to_scan;
  	unsigned long freed = 0;

@@ -734,7 +734,7 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
  static unsigned long bch_mca_count(struct shrinker *shrink,
  				   struct shrink_control *sc)
  {
-	struct cache_set *c = container_of(shrink, struct cache_set, shrink);
+	struct cache_set *c = shrink->private_data;
  
  	if (c->shrinker_disabled)
  		return 0;

@@ -752,8 +752,8 @@ void bch_btree_cache_free(struct cache_set *c)
  
  	closure_init_stack(&cl);
  
-	if (c->shrink.list.next)
-		unregister_shrinker(&c->shrink);
+	if (c->shrink)
+		shrinker_unregister(c->shrink);
  
  	mutex_lock(&c->bucket_lock);
  

@@ -828,14 +828,19 @@ int bch_btree_cache_alloc(struct cache_set *c)
  		c->verify_data = NULL;
  #endif
  
-	c->shrink.count_objects = bch_mca_count;
-	c->shrink.scan_objects = bch_mca_scan;
-	c->shrink.seeks = 4;
-	c->shrink.batch = c->btree_pages * 2;
+	c->shrink = shrinker_alloc(0, "md-bcache:%pU", c->set_uuid);
+	if (!c->shrink) {
+		pr_warn("bcache: %s: could not allocate shrinker\n", __func__);
+		return -ENOMEM;

+	}
+
+	c->shrink->count_objects = bch_mca_count;
+	c->shrink->scan_objects = bch_mca_scan;
+	c->shrink->seeks = 4;
+	c->shrink->batch = c->btree_pages * 2;
+	c->shrink->private_data = c;
  
-	if (register_shrinker(&c->shrink, "md-bcache:%pU", c->set_uuid))
-		pr_warn("bcache: %s: could not register shrinker\n",
-				__func__);
+	shrinker_register(c->shrink);
  
  	return 0;
  }

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 0e2c1880f60b..45d8af755de6 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c

@@ -866,7 +866,8 @@ STORE(__bch_cache_set)
  
  		sc.gfp_mask = GFP_KERNEL;
  		sc.nr_to_scan = strtoul_or_return(buf);
-		c->shrink.scan_objects(&c->shrink, &sc);
+		if (c->shrink)
+			c->shrink->scan_objects(c->shrink, &sc);
  	}
  
  	sysfs_strtoul_clamp(congested_read_threshold_us,