trace: handle key being freed while suspended.

This happens with autoclean, which does a datastore request then frees
the parent command without waiting for a response (see clean_finished).

This leaks a trace, and causes a crash if the pointer is later reused.

My solution is to create a trace variant which declares the trace key
to be a tal ptr and then we can clean up in the destructor if this happens.
This fixes the issue for me.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: autoclean: fixed occasional crash when tracepoints compiled in.

Author: rustyrussell

common/trace.c

@@ -373,6 +373,28 @@ void trace_span_suspend_(const void *key, const char *lbl)
 	DTRACE_PROBE1(lightningd, span_suspend, span->id);
 }
 
+static void destroy_trace_span(const void *key)
+{
+	size_t numkey = trace_key(key);
+	struct span *span = trace_span_find(numkey);
+
+	/* It's usually ended normally. */
+	if (!span)
+		return;
+
+	/* Otherwise resume so we can terminate it */
+	trace_span_resume(key);
+	trace_span_end(key);
+}
+
+void trace_span_suspend_may_free_(const void *key, const char *lbl)
+{
+	if (disable_trace)
+		return;
+	trace_span_suspend_(key, lbl);
+	tal_add_destructor(key, destroy_trace_span);
+}
+
 void trace_span_resume_(const void *key, const char *lbl)
 {
 	if (disable_trace)
@@ -395,6 +417,7 @@ void trace_cleanup(void)
 void trace_span_start(const char *name, const void *key) {}
 void trace_span_end(const void *key) {}
 void trace_span_suspend_(const void *key, const char *lbl) {}
+void trace_span_suspend_may_free_(const void *key, const char *lbl) {}
 void trace_span_resume_(const void *key, const char *lbl) {}
 void trace_span_tag(const void *key, const char *name, const char *value) {}
 void trace_cleanup(void) {}

common/trace.h

@@ -15,8 +15,10 @@ void trace_span_remote(u8 trace_id[TRACE_ID_SIZE], u8 span_id[SPAN_ID_SIZE]);
 
 #define TRACE_LBL __FILE__ ":" stringify(__LINE__)
 void trace_span_suspend_(const void *key, const char *lbl);
+void trace_span_suspend_may_free_(const void *key, const char *lbl);
 void trace_span_resume_(const void *key, const char *lbl);
 #define trace_span_suspend(key) trace_span_suspend_(key, TRACE_LBL)
+#define trace_span_suspend_may_free(key) trace_span_suspend_may_free_(key, TRACE_LBL)
 #define trace_span_resume(key) trace_span_resume_(key, TRACE_LBL)
 
 #endif /* LIGHTNING_COMMON_TRACE_H */

plugins/libplugin.c

@@ -1110,7 +1110,7 @@ send_outreq(const struct out_req *req)
 	 * callback. */
 	trace_span_start("jsonrpc", req);
 	trace_span_tag(req, "id", req->id);
-	trace_span_suspend(req);
+	trace_span_suspend_may_free(req);
 
 	ld_rpc_send(req->cmd->plugin, req->js);
 	notleak_with_children(req->cmd);