bcachefs: Tweak btree cache helpers for use by btree node scan

btree node scan needs to not use the btree node cache: that causes
interference from prior failed reads and parallel workers.

Instead we need to allocate btree nodes that don't live in the btree
cache, so that we can call bch2_btree_node_read_done() directly.

This patch tweaks the low level helpers so they don't touch the btree
cache lists.

Cc: Nikita Ofitserov <himikof@gmail.com>
Reviewed-by: Nikita Ofitserov <himikof@gmail.com>
Reported-and-tested-by: Edoardo Codeglia <bcachefs@404.blue>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: Kent Overstreet

fs/bcachefs/btree_cache.c

@@ -85,7 +85,7 @@ void bch2_btree_node_to_freelist(struct bch_fs *c, struct btree *b)
 	six_unlock_intent(&b->c.lock);
 }
 
-static void __btree_node_data_free(struct btree_cache *bc, struct btree *b)
+void __btree_node_data_free(struct btree *b)
 {
 	BUG_ON(!list_empty(&b->list));
 	BUG_ON(btree_node_hashed(b));
@@ -112,16 +112,17 @@ static void __btree_node_data_free(struct btree_cache *bc, struct btree *b)
 	munmap(b->aux_data, btree_aux_data_bytes(b));
 #endif
 	b->aux_data = NULL;
-
-	btree_node_to_freedlist(bc, b);
 }
 
 static void btree_node_data_free(struct btree_cache *bc, struct btree *b)
 {
 	BUG_ON(list_empty(&b->list));
 	list_del_init(&b->list);
+
+	__btree_node_data_free(b);
+
 	--bc->nr_freeable;
-	__btree_node_data_free(bc, b);
+	btree_node_to_freedlist(bc, b);
 }
 
 static int bch2_btree_cache_cmp_fn(struct rhashtable_compare_arg *arg,
@@ -185,10 +186,7 @@ static struct btree *__btree_node_mem_alloc(struct bch_fs *c, gfp_t gfp)
 
 struct btree *__bch2_btree_node_mem_alloc(struct bch_fs *c)
 {
-	struct btree_cache *bc = &c->btree_cache;
-	struct btree *b;
-
-	b = __btree_node_mem_alloc(c, GFP_KERNEL);
+	struct btree *b = __btree_node_mem_alloc(c, GFP_KERNEL);
 	if (!b)
 		return NULL;
 
@@ -198,8 +196,6 @@ struct btree *__bch2_btree_node_mem_alloc(struct bch_fs *c)
 	}
 
 	bch2_btree_lock_init(&b->c, 0, GFP_KERNEL);
-
-	__bch2_btree_node_to_freelist(bc, b);
 	return b;
 }
 
@@ -524,7 +520,8 @@ static unsigned long bch2_btree_cache_scan(struct shrinker *shrink,
 			--touched;;
 		} else if (!btree_node_reclaim(c, b)) {
 			__bch2_btree_node_hash_remove(bc, b);
-			__btree_node_data_free(bc, b);
+			__btree_node_data_free(b);
+			btree_node_to_freedlist(bc, b);
 
 			freed++;
 			bc->nr_freed++;
@@ -652,9 +649,12 @@ int bch2_fs_btree_cache_init(struct bch_fs *c)
 
 	bch2_recalc_btree_reserve(c);
 
-	for (i = 0; i < bc->nr_reserve; i++)
-		if (!__bch2_btree_node_mem_alloc(c))
+	for (i = 0; i < bc->nr_reserve; i++) {
+		struct btree *b = __bch2_btree_node_mem_alloc(c);
+		if (!b)
 			goto err;
+		__bch2_btree_node_to_freelist(bc, b);
+	}
 
 	list_splice_init(&bc->live[0].list, &bc->freeable);
 

fs/bcachefs/btree_cache.h

@@ -30,6 +30,7 @@ void bch2_btree_node_update_key_early(struct btree_trans *, enum btree_id, unsig
 void bch2_btree_cache_cannibalize_unlock(struct btree_trans *);
 int bch2_btree_cache_cannibalize_lock(struct btree_trans *, struct closure *);
 
+void __btree_node_data_free(struct btree *);
 struct btree *__bch2_btree_node_mem_alloc(struct bch_fs *);
 struct btree *bch2_btree_node_mem_alloc(struct btree_trans *, bool);
 

fs/bcachefs/debug.c

@@ -153,8 +153,6 @@ void __bch2_btree_verify(struct bch_fs *c, struct btree *b)
 		c->verify_data = __bch2_btree_node_mem_alloc(c);
 		if (!c->verify_data)
 			goto out;
-
-		list_del_init(&c->verify_data->list);
 	}
 
 	BUG_ON(b->nsets != 1);