trace: double allocation if we run out.

This doesn't happen very often, but can with autoclean.

However, we rarely traverse to the end, since we always expect to find
what we're looking for, and we fill from the front.  So even a large
array (unless it's used) is fine.

Subtle: when we injected a parent, we used "active_spans" as the (arbitrary)
key.  That can now change with reallocation, and so if that memory were reused
we could have a key clash.  So we use "&active_spans" which doesn't change.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Author: rustyrussell

common/trace.c

@@ -2,7 +2,6 @@
 #include <assert.h>
 #include <ccan/endian/endian.h>
 #include <ccan/err/err.h>
-#include <ccan/htable/htable.h>
 #include <ccan/str/hex/hex.h>
 #include <ccan/tal/str/str.h>
 #include <ccan/tal/tal.h>
@@ -18,8 +17,6 @@
 #if HAVE_USDT
   #include <sys/sdt.h>
 
-#define MAX_ACTIVE_SPANS 128
-
 /* The traceperent format is defined in W3C Trace Context RFC[1].
  * Its format is defined as
  *
@@ -123,7 +120,7 @@ static void trace_inject_traceparent(void)
 	current = trace_span_slot();
 	assert(current);
 
-	init_span(current, trace_key(active_spans), "", NULL);
+	init_span(current, trace_key(&active_spans), "", NULL);
 	assert(current && !current->parent);
 
 	if (!hex_decode(traceparent + 3, 16, &trace_hi, sizeof(trace_hi))
@@ -145,7 +142,7 @@ static void trace_inject_traceparent(void)
 /** Quickly print out the entries in the `active_spans`. */
 static void trace_spans_print(void)
 {
-	for (size_t j = 0; j < MAX_ACTIVE_SPANS; j++) {
+	for (size_t j = 0; j < tal_count(active_spans); j++) {
 		struct span *s = &active_spans[j], *parent = s->parent;
 		TRACE_DBG(" > %zu: %s (key=%zu, parent=%s, "
 			  "parent_key=%zu)\n",
@@ -156,17 +153,17 @@ static void trace_spans_print(void)
 
 /** Small helper to check for consistency in the linking. The idea is
  * that we should be able to reach the root (a span without a
- * `parent`) in less than `MAX_ACTIVE_SPANS` steps. */
+ * `parent`) in less than the number of spans. */
 static void trace_check_tree(void)
 {
 	/* `current` is either NULL or a valid entry. */
 
 	/* Walk the tree structure from leaves to their roots. It
-	 * should not take more than `MAX_ACTIVE_SPANS`. */
+	 * should not take more than the number of spans. */
 	struct span *c;
-	for (size_t i = 0; i < MAX_ACTIVE_SPANS; i++) {
+	for (size_t i = 0; i < tal_count(active_spans); i++) {
 		c = &active_spans[i];
-		for (int j = 0; j < MAX_ACTIVE_SPANS; j++)
+		for (int j = 0; j < tal_count(active_spans); j++)
 			if (c->parent == NULL)
 				break;
 			else
@@ -189,7 +186,8 @@ static void trace_init(void)
 	const char *dev_trace_file;
 	if (active_spans)
 		return;
-	active_spans = calloc(MAX_ACTIVE_SPANS, sizeof(struct span));
+
+	active_spans = notleak(tal_arrz(NULL, struct span, 1));
 
 	current = NULL;
 	dev_trace_file = getenv("DEV_CLN_TRACE_FILE");
@@ -213,7 +211,7 @@ static size_t trace_key(const void *key)
 
 static struct span *trace_span_find(size_t key)
 {
-	for (size_t i = 0; i < MAX_ACTIVE_SPANS; i++)
+	for (size_t i = 0; i < tal_count(active_spans); i++)
 		if (active_spans[i].key == key)
 			return &active_spans[i];
 
@@ -232,14 +230,12 @@ static struct span *trace_span_slot(void)
 	 * that, and we should get an empty slot. */
 	struct span *s = trace_span_find(0);
 
-	/* Might end up here if we have more than MAX_ACTIVE_SPANS
-	 * concurrent spans. */
+	/* In the unlikely case this fails, double it */
 	if (!s) {
-		fprintf(stderr, "%u: out of spans, disabling tracing\n", getpid());
-		for (size_t i = 0; i < MAX_ACTIVE_SPANS; i++)
-			trace_span_clear(&active_spans[i]);
-		disable_trace = true;
-		return NULL;
+		TRACE_DBG("%u: out of %zu spans, doubling!\n",
+			  getpid(), tal_count(active_spans));
+		tal_resizez(&active_spans, tal_count(active_spans) * 2);
+		s = trace_span_find(0);
 	}
 	assert(s->parent == NULL);
 
@@ -460,8 +456,7 @@ void trace_span_resume_(const void *key, const char *lbl)
 
 void trace_cleanup(void)
 {
-	free(active_spans);
-	active_spans = NULL;
+	active_spans = tal_free(active_spans);
 }
 
 #else /* HAVE_USDT */