bcachefs: Kill nodes_intent_locked

Previously, we used two different bit arrays for tracking held btree
node locks. This patch switches to an array of two bit integers, which
will let us track, in a future patch, when we hold a write lock.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/btree_iter.c

@@ -1519,7 +1519,6 @@ static struct btree_path *btree_path_alloc(struct btree_trans *trans,
 	path->ref		= 0;
 	path->intent_ref	= 0;
 	path->nodes_locked	= 0;
-	path->nodes_intent_locked = 0;
 
 	btree_path_list_add(trans, pos, path);
 	trans->paths_sorted = false;
@@ -1574,7 +1573,6 @@ struct btree_path *bch2_path_get(struct btree_trans *trans,
 		path->level			= level;
 		path->locks_want		= locks_want;
 		path->nodes_locked		= 0;
-		path->nodes_intent_locked	= 0;
 		for (i = 0; i < ARRAY_SIZE(path->l); i++)
 			path->l[i].b		= ERR_PTR(-BCH_ERR_no_btree_node_init);
 #ifdef CONFIG_BCACHEFS_DEBUG

fs/bcachefs/btree_locking.h

@@ -37,14 +37,7 @@ enum btree_node_locked_type {
 static inline int btree_node_locked_type(struct btree_path *path,
 					 unsigned level)
 {
-	/*
-	 * We're relying on the fact that if nodes_intent_locked is set
-	 * nodes_locked must be set as well, so that we can compute without
-	 * branches:
-	 */
-	return BTREE_NODE_UNLOCKED +
-		((path->nodes_locked >> level) & 1) +
-		((path->nodes_intent_locked >> level) & 1);
+	return BTREE_NODE_UNLOCKED + ((path->nodes_locked >> (level << 1)) & 3);
 }
 
 static inline bool btree_node_intent_locked(struct btree_path *path,
@@ -65,20 +58,15 @@ static inline bool btree_node_locked(struct btree_path *path, unsigned level)
 }
 
 static inline void mark_btree_node_locked_noreset(struct btree_path *path,
-					  unsigned level,
-					  enum btree_node_locked_type type)
+						  unsigned level,
+						  enum btree_node_locked_type type)
 {
 	/* relying on this to avoid a branch */
 	BUILD_BUG_ON(SIX_LOCK_read   != 0);
 	BUILD_BUG_ON(SIX_LOCK_intent != 1);
 
-	path->nodes_locked &= ~(1 << level);
-	path->nodes_intent_locked &= ~(1 << level);
-
-	if (type != BTREE_NODE_UNLOCKED) {
-		path->nodes_locked |= 1 << level;
-		path->nodes_intent_locked |= type << level;
-	}
+	path->nodes_locked &= ~(3U << (level << 1));
+	path->nodes_locked |= (type + 1) << (level << 1);
 }
 
 static inline void mark_btree_node_unlocked(struct btree_path *path,
@@ -162,12 +150,12 @@ static inline void btree_node_unlock(struct btree_trans *trans,
 
 static inline int btree_path_lowest_level_locked(struct btree_path *path)
 {
-	return __ffs(path->nodes_locked);
+	return __ffs(path->nodes_locked) >> 1;
 }
 
 static inline int btree_path_highest_level_locked(struct btree_path *path)
 {
-	return __fls(path->nodes_locked);
+	return __fls(path->nodes_locked) >> 1;
 }
 
 static inline void __bch2_btree_path_unlock(struct btree_trans *trans,

fs/bcachefs/btree_types.h

@@ -232,9 +232,8 @@ struct btree_path {
 	 */
 	bool			should_be_locked:1;
 	unsigned		level:3,
-				locks_want:4,
-				nodes_locked:4,
-				nodes_intent_locked:4;
+				locks_want:4;
+	u8			nodes_locked;
 
 	struct btree_path_level {
 		struct btree	*b;