trace-cmd: Move clock_context_init() out of pthreads

If the clock_context_init() fails, it can cause the communications between
the host and guest to hang without any clue to why it happened. I spent
several hours debugging this.

There's no reason that the clock_context_init() needs to be called in the
pthread. Do that before creating the threads, and move the proto into the
tsync structure itself.

Now when it fails, more can be known at the time it happens.

Link: https://lore.kernel.org/linux-trace-devel/20220707190726.3f1c6b4d@gandalf.local.home

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

2 files changed, 19 insertions, 20 deletions

diff --git a/lib/trace-cmd/include/trace-tsync-local.h b/lib/trace-cmd/include/trace-tsync-local.h
index 5bbc1db6..27baa593 100644
--- a/lib/trace-cmd/include/trace-tsync-local.h
+++ b/lib/trace-cmd/include/trace-tsync-local.h
@@ -8,6 +8,8 @@
 
 #include <stdbool.h>
 
+struct tsync_proto;
+
 struct tracecmd_time_sync {
 	pthread_t			thread;
 	bool				thread_running;
@@ -19,6 +21,7 @@ struct tracecmd_time_sync {
 	pthread_barrier_t		first_sync;
 	char				*clock_str;
 	struct tracecmd_msg_handle	*msg_handle;
+	struct tsync_proto		*proto;
 	void				*context;
 	int				guest_pid;
 	int				vcpu_count;
diff --git a/lib/trace-cmd/trace-timesync.c b/lib/trace-cmd/trace-timesync.c
index 8d4e977f..bc643098 100644
--- a/lib/trace-cmd/trace-timesync.c
+++ b/lib/trace-cmd/trace-timesync.c
@@ -382,8 +382,7 @@ clock_synch_delete_instance(struct tracefs_instance *inst)
 	tracefs_instance_free(inst);
 }
 
-static int clock_context_init(struct tracecmd_time_sync *tsync,
-			      struct tsync_proto **proto, bool guest)
+static int clock_context_init(struct tracecmd_time_sync *tsync, bool guest)
 {
 	struct clock_sync_context *clock = NULL;
 	struct tsync_proto *protocol;
@@ -417,7 +416,7 @@ static int clock_context_init(struct tracecmd_time_sync *tsync,
 	if (protocol->clock_sync_init && protocol->clock_sync_init(tsync) < 0)
 		goto error;
 
-	*proto = protocol;
+	tsync->proto = protocol;
 
 	return 0;
 error:
@@ -539,9 +538,9 @@ static void restore_pin_to_cpu(cpu_set_t *mask)
 	CPU_FREE(mask);
 }
 
-static int tsync_send(struct tracecmd_time_sync *tsync,
-		      struct tsync_proto *proto, unsigned int cpu)
+static int tsync_send(struct tracecmd_time_sync *tsync, unsigned int cpu)
 {
+	struct tsync_proto *proto = tsync->proto;
 	cpu_set_t *old_set = NULL;
 	long long timestamp = 0;
 	long long scaling = 0;
@@ -561,16 +560,11 @@ static void tsync_with_host(struct tracecmd_time_sync *tsync)
 {
 	char protocol[TRACECMD_TSYNC_PNAME_LENGTH];
 	struct tsync_probe_request_msg probe;
-	struct tsync_proto *proto;
 	unsigned int command;
 	unsigned int size;
 	char *msg;
 	int ret;
 
-	clock_context_init(tsync, &proto, true);
-	if (!tsync->context)
-		return;
-
 	msg = (char *)&probe;
 	size = sizeof(probe);
 	while (true) {
@@ -582,7 +576,7 @@ static void tsync_with_host(struct tracecmd_time_sync *tsync)
 		if (ret || strncmp(protocol, TRACECMD_TSYNC_PROTO_NONE, TRACECMD_TSYNC_PNAME_LENGTH) ||
 		    command != TRACECMD_TIME_SYNC_CMD_PROBE)
 			break;
-		ret = tsync_send(tsync, proto, probe.cpu);
+		ret = tsync_send(tsync, probe.cpu);
 		if (ret)
 			break;
 	}
@@ -630,8 +624,9 @@ static int record_sync_sample(struct clock_sync_offsets *offsets, int array_step
 }
 
 static int tsync_get_sample(struct tracecmd_time_sync *tsync, unsigned int cpu,
-			    struct tsync_proto *proto, int array_step)
+			    int array_step)
 {
+	struct tsync_proto *proto = tsync->proto;
 	struct clock_sync_context *clock;
 	long long timestamp = 0;
 	long long scaling = 0;
@@ -672,19 +667,12 @@ static int tsync_with_guest(struct tracecmd_time_sync *tsync)
 {
 	struct tsync_probe_request_msg probe;
 	int ts_array_size = CLOCK_TS_ARRAY;
-	struct tsync_proto *proto;
 	struct timespec timeout;
 	bool first = true;
 	bool end = false;
 	int ret;
 	int i;
 
-	clock_context_init(tsync, &proto, false);
-	if (!tsync->context) {
-		pthread_barrier_wait(&tsync->first_sync);
-		return -1;
-	}
-
 	if (tsync->loop_interval > 0 &&
 	    tsync->loop_interval < (CLOCK_TS_ARRAY * 1000))
 		ts_array_size = (CLOCK_TS_ARRAY * 1000) / tsync->loop_interval;
@@ -697,7 +685,7 @@ static int tsync_with_guest(struct tracecmd_time_sync *tsync)
 							  TRACECMD_TSYNC_PROTO_NONE,
 							  TRACECMD_TIME_SYNC_CMD_PROBE,
 							  sizeof(probe), (char *)&probe);
-			ret = tsync_get_sample(tsync, i, proto, ts_array_size);
+			ret = tsync_get_sample(tsync, i, ts_array_size);
 			if (ret)
 				break;
 		}
@@ -793,6 +781,10 @@ tracecmd_tsync_with_guest(unsigned long long trace_id, int loop_interval,
 	pthread_attr_init(&attrib);
 	pthread_attr_setdetachstate(&attrib, PTHREAD_CREATE_JOINABLE);
 
+	clock_context_init(tsync, false);
+	if (!tsync->context)
+		goto error;
+
 	ret = pthread_create(&tsync->thread, &attrib, tsync_host_thread, tsync);
 	if (ret)
 		goto error;
@@ -983,6 +975,10 @@ tracecmd_tsync_with_host(int fd, const char *proto, const char *clock,
 	tsync->vcpu_count = tracecmd_count_cpus();
 	pthread_attr_setdetachstate(&attrib, PTHREAD_CREATE_JOINABLE);
 
+	clock_context_init(tsync, true);
+	if (!tsync->context)
+		goto error;
+
 	ret = pthread_create(&tsync->thread, &attrib, tsync_agent_thread, tsync);
 	if (ret) {
 		pthread_attr_destroy(&attrib);