bcachefs: Add tracepoint & counter for btree split race

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs_format.h

@@ -1478,7 +1478,8 @@ struct bch_sb_field_disk_groups {
 	x(transaction_commit,				72)	\
 	x(write_super,					73)	\
 	x(trans_restart_would_deadlock_recursion_limit,	74)	\
-	x(trans_restart_write_buffer_flush,		75)
+	x(trans_restart_write_buffer_flush,		75)	\
+	x(trans_restart_split_race,			76)
 
 enum bch_persistent_counters {
 #define x(t, n, ...) BCH_COUNTER_##t,

fs/bcachefs/btree_update_interior.c

@@ -1717,8 +1717,10 @@ static int bch2_btree_insert_node(struct btree_update *as, struct btree_trans *t
 	 * We could attempt to avoid the transaction restart, by calling
 	 * bch2_btree_path_upgrade() and allocating more nodes:
 	 */
-	if (b->c.level >= as->update_level)
+	if (b->c.level >= as->update_level) {
+		trace_and_count(c, trans_restart_split_race, trans, _THIS_IP_);
 		return btree_trans_restart(trans, BCH_ERR_transaction_restart_split_race);
+	}
 
 	return btree_split(as, trans, path, b, keys, flags);
 }

fs/bcachefs/trace.h

@@ -837,6 +837,12 @@ DEFINE_EVENT(transaction_event,	trans_restart_injected,
 	TP_ARGS(trans, caller_ip)
 );
 
+DEFINE_EVENT(transaction_event,	trans_restart_split_race,
+	TP_PROTO(struct btree_trans *trans,
+		 unsigned long caller_ip),
+	TP_ARGS(trans, caller_ip)
+);
+
 DEFINE_EVENT(transaction_event,	trans_blocked_journal_reclaim,
 	TP_PROTO(struct btree_trans *trans,
 		 unsigned long caller_ip),