bcachefs: Add more assertions for locking btree iterators out of order

btree_path_traverse_all() traverses btree iterators in sorted order, and
thus shouldn't see transaction restarts due to potential deadlocks - but
sometimes we do. This patch adds some more assertions and tracks some
more state to help track this down.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/btree_iter.c

@@ -17,8 +17,6 @@
 
 #include <linux/prefetch.h>
 
-static inline void btree_trans_sort_paths(struct btree_trans *);
-
 static inline void btree_path_list_remove(struct btree_trans *, struct btree_path *);
 static inline void btree_path_list_add(struct btree_trans *, struct btree_path *,
 				       struct btree_path *);
@@ -159,7 +157,7 @@ bool __bch2_btree_node_relock(struct btree_trans *trans,
 	if (six_relock_type(&b->c.lock, want, path->l[level].lock_seq) ||
 	    (btree_node_lock_seq_matches(path, b, level) &&
 	     btree_node_lock_increment(trans, b, level, want))) {
-		mark_btree_node_locked(path, level, want);
+		mark_btree_node_locked(trans, path, level, want);
 		return true;
 	} else {
 		return false;
@@ -195,7 +193,7 @@ static bool bch2_btree_node_upgrade(struct btree_trans *trans,
 
 	return false;
 success:
-	mark_btree_node_intent_locked(path, level);
+	mark_btree_node_intent_locked(trans, path, level);
 	return true;
 }
 
@@ -1078,7 +1076,7 @@ void bch2_trans_node_add(struct btree_trans *trans, struct btree *b)
 			t = btree_lock_want(path, b->c.level);
 			if (t != BTREE_NODE_UNLOCKED) {
 				six_lock_increment(&b->c.lock, (enum six_lock_type) t);
-				mark_btree_node_locked(path, b->c.level, (enum six_lock_type) t);
+				mark_btree_node_locked(trans, path, b->c.level, (enum six_lock_type) t);
 			}
 
 			btree_path_level_init(trans, path, b);
@@ -1167,7 +1165,7 @@ static inline int btree_path_lock_root(struct btree_trans *trans,
 			for (i = path->level + 1; i < BTREE_MAX_DEPTH; i++)
 				path->l[i].b = NULL;
 
-			mark_btree_node_locked(path, path->level, lock_type);
+			mark_btree_node_locked(trans, path, path->level, lock_type);
 			btree_path_level_init(trans, path, b);
 			return 0;
 		}
@@ -1259,7 +1257,7 @@ static __always_inline int btree_path_down(struct btree_trans *trans,
 	if (unlikely(ret))
 		goto err;
 
-	mark_btree_node_locked(path, level, lock_type);
+	mark_btree_node_locked(trans, path, level, lock_type);
 	btree_path_level_init(trans, path, b);
 
 	if (tmp.k->k.type == KEY_TYPE_btree_ptr_v2 &&
@@ -1340,6 +1338,9 @@ static int __btree_path_traverse_all(struct btree_trans *trans, int ret,
 		path = trans->paths + trans->sorted[i];
 
 		EBUG_ON(!(trans->paths_allocated & (1ULL << path->idx)));
+#ifdef CONFIG_BCACHEFS_DEBUG
+		trans->traverse_all_idx = path->idx;
+#endif
 
 		ret = btree_path_traverse_one(trans, path, 0, _THIS_IP_);
 		if (ret)
@@ -1361,6 +1362,9 @@ static int __btree_path_traverse_all(struct btree_trans *trans, int ret,
 out:
 	bch2_btree_cache_cannibalize_unlock(c);
 
+#ifdef CONFIG_BCACHEFS_DEBUG
+	trans->traverse_all_idx = U8_MAX;
+#endif
 	trans->in_traverse_all = false;
 
 	trace_trans_traverse_all(trans->ip, trace_ip);
@@ -2319,13 +2323,9 @@ static void btree_trans_verify_sorted_refs(struct btree_trans *trans)
 		BUG_ON(trans->paths[idx].sorted_idx != i);
 	}
 }
-#else
-static inline void btree_trans_verify_sorted_refs(struct btree_trans *trans) {}
-#endif
 
 static void btree_trans_verify_sorted(struct btree_trans *trans)
 {
-#ifdef CONFIG_BCACHEFS_DEBUG
 	struct btree_path *path, *prev = NULL;
 	unsigned i;
 
@@ -2333,14 +2333,22 @@ static void btree_trans_verify_sorted(struct btree_trans *trans)
 		BUG_ON(prev && btree_path_cmp(prev, path) > 0);
 		prev = path;
 	}
-#endif
 }
+#else
+static inline void btree_trans_verify_sorted_refs(struct btree_trans *trans) {}
+static inline void btree_trans_verify_sorted(struct btree_trans *trans) {}
+#endif
 
-static noinline void __btree_trans_sort_paths(struct btree_trans *trans)
+void __bch2_btree_trans_sort_paths(struct btree_trans *trans)
 {
 	int i, l = 0, r = trans->nr_sorted, inc = 1;
 	bool swapped;
 
+	btree_trans_verify_sorted_refs(trans);
+
+	if (trans->paths_sorted)
+		goto out;
+
 	/*
 	 * Cocktail shaker sort: this is efficient because iterators will be
 	 * mostly sorteda.
@@ -2368,22 +2376,10 @@ static noinline void __btree_trans_sort_paths(struct btree_trans *trans)
 	} while (swapped);
 
 	trans->paths_sorted = true;
-
+out:
 	btree_trans_verify_sorted(trans);
 }
 
-static inline void btree_trans_sort_paths(struct btree_trans *trans)
-{
-	btree_trans_verify_sorted_refs(trans);
-
-	if (trans->paths_sorted) {
-		if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG))
-			btree_trans_verify_sorted(trans);
-		return;
-	}
-	__btree_trans_sort_paths(trans);
-}
-
 static inline void btree_path_list_remove(struct btree_trans *trans,
 					  struct btree_path *path)
 {
@@ -2410,7 +2406,7 @@ static inline void btree_path_list_add(struct btree_trans *trans,
 {
 	unsigned i;
 
-	path->sorted_idx = pos ? pos->sorted_idx + 1 : 0;
+	path->sorted_idx = pos ? pos->sorted_idx + 1 : trans->nr_sorted;
 
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 	memmove_u64s_up_small(trans->sorted + path->sorted_idx + 1,

fs/bcachefs/btree_iter.h

@@ -57,6 +57,16 @@ static inline int btree_iter_err(const struct btree_iter *iter)
 
 /* Iterate over paths within a transaction: */
 
+void __bch2_btree_trans_sort_paths(struct btree_trans *);
+
+static inline void btree_trans_sort_paths(struct btree_trans *trans)
+{
+	if (!IS_ENABLED(CONFIG_BCACHEFS_DEBUG) &&
+	    trans->paths_sorted)
+		return;
+	__bch2_btree_trans_sort_paths(trans);
+}
+
 static inline struct btree_path *
 __trans_next_path(struct btree_trans *trans, unsigned idx)
 {

fs/bcachefs/btree_key_cache.c

@@ -297,7 +297,7 @@ int bch2_btree_path_traverse_cached(struct btree_trans *trans, struct btree_path
 		if (!ck)
 			goto retry;
 
-		mark_btree_node_locked(path, 0, SIX_LOCK_intent);
+		mark_btree_node_locked(trans, path, 0, SIX_LOCK_intent);
 		path->locks_want = 1;
 	} else {
 		enum six_lock_type lock_want = __btree_lock_want(path, 0);
@@ -319,7 +319,7 @@ int bch2_btree_path_traverse_cached(struct btree_trans *trans, struct btree_path
 			goto retry;
 		}
 
-		mark_btree_node_locked(path, 0, lock_want);
+		mark_btree_node_locked(trans, path, 0, lock_want);
 	}
 
 	path->l[0].lock_seq	= ck->c.lock.state.seq;

fs/bcachefs/btree_locking.h

@@ -57,7 +57,8 @@ static inline void mark_btree_node_unlocked(struct btree_path *path,
 	path->nodes_intent_locked &= ~(1 << level);
 }
 
-static inline void mark_btree_node_locked(struct btree_path *path,
+static inline void mark_btree_node_locked(struct btree_trans *trans,
+					  struct btree_path *path,
 					  unsigned level,
 					  enum six_lock_type type)
 {
@@ -67,12 +68,20 @@ static inline void mark_btree_node_locked(struct btree_path *path,
 
 	path->nodes_locked |= 1 << level;
 	path->nodes_intent_locked |= type << level;
+#ifdef CONFIG_BCACHEFS_DEBUG
+	path->ip_locked = _RET_IP_;
+	btree_trans_sort_paths(trans);
+	BUG_ON(trans->in_traverse_all &&
+	       trans->traverse_all_idx != U8_MAX &&
+	       path->sorted_idx > trans->paths[trans->traverse_all_idx].sorted_idx);
+#endif
 }
 
-static inline void mark_btree_node_intent_locked(struct btree_path *path,
+static inline void mark_btree_node_intent_locked(struct btree_trans *trans,
+						 struct btree_path *path,
 						 unsigned level)
 {
-	mark_btree_node_locked(path, level, SIX_LOCK_intent);
+	mark_btree_node_locked(trans, path, level, SIX_LOCK_intent);
 }
 
 static inline enum six_lock_type __btree_lock_want(struct btree_path *path, int level)
@@ -111,6 +120,9 @@ static inline void __bch2_btree_path_unlock(struct btree_path *path)
 
 	while (path->nodes_locked)
 		btree_node_unlock(path, __ffs(path->nodes_locked));
+#ifdef CONFIG_BCACHEFS_DEBUG
+	path->ip_locked = 0;
+#endif
 }
 
 static inline enum bch_time_stats lock_to_time_stat(enum six_lock_type type)

fs/bcachefs/btree_types.h

@@ -255,6 +255,7 @@ struct btree_path {
 	}			l[BTREE_MAX_DEPTH];
 #ifdef CONFIG_BCACHEFS_DEBUG
 	unsigned long		ip_allocated;
+	unsigned long		ip_locked;
 #endif
 };
 
@@ -368,6 +369,7 @@ struct btree_trans {
 	struct bpos		locking_pos;
 	u8			locking_btree_id;
 	u8			locking_level;
+	u8			traverse_all_idx;
 	pid_t			pid;
 #endif
 	unsigned long		ip;