bcache: Rework btree cache reserve handling

This changes the bucket allocation reserves to use _real_ reserves - separate
freelists - instead of watermarks, which if nothing else makes the current code
saner to reason about and is going to be important in the future when we add
support for multiple btrees.

It also adds btree_check_reserve(), which checks (and locks) the reserves for
both bucket allocation and memory allocation for btree nodes; the old code just
kinda sorta assumed that since (e.g. for btree node splits) it had the root
locked and that meant no other threads could try to make use of the same
reserve; this technically should have been ok for memory allocation (we should
always have a reserve for memory allocation (the btree node cache is used as a
reserve and we preallocate it)), but multiple btrees will mean that locking the
root won't be sufficient anymore, and for the bucket allocation reserve it was
technically possible for the old code to deadlock.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

1 files changed, 3 insertions, 10 deletions

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 307fe37..2d4a562 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1495,14 +1495,13 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
 
 	sema_init(&c->sb_write_mutex, 1);
 	mutex_init(&c->bucket_lock);
-	init_waitqueue_head(&c->try_wait);
+	init_waitqueue_head(&c->btree_cache_wait);
 	init_waitqueue_head(&c->bucket_wait);
 	sema_init(&c->uuid_write_mutex, 1);
 
 	spin_lock_init(&c->btree_gc_time.lock);
 	spin_lock_init(&c->btree_split_time.lock);
 	spin_lock_init(&c->btree_read_time.lock);
-	spin_lock_init(&c->try_harder_time.lock);
 
 	bch_moving_init_cache_set(c);
 
@@ -1591,7 +1590,7 @@ static void run_cache_set(struct cache_set *c)
 			goto err;
 
 		err = "error reading btree root";
-		c->root = bch_btree_node_get(c, k, j->btree_level, true);
+		c->root = bch_btree_node_get(c, NULL, k, j->btree_level, true);
 		if (IS_ERR_OR_NULL(c->root))
 			goto err;
 
@@ -1666,7 +1665,7 @@ static void run_cache_set(struct cache_set *c)
 			goto err;
 
 		err = "cannot allocate new btree root";
-		c->root = bch_btree_node_alloc(c, 0, true);
+		c->root = bch_btree_node_alloc(c, NULL, 0);
 		if (IS_ERR_OR_NULL(c->root))
 			goto err;
 
@@ -1847,13 +1846,7 @@ static int cache_alloc(struct cache_sb *sb, struct cache *ca)
 	for_each_bucket(b, ca)
 		atomic_set(&b->pin, 0);
 
-	if (bch_cache_allocator_init(ca))
-		goto err;
-
 	return 0;
-err:
-	kobject_put(&ca->kobj);
-	return -ENOMEM;
 }
 
 static void register_cache(struct cache_sb *sb, struct page *sb_page,