Fix hsaKmtOpen incorrectly doing nothing in some fork scenarios

Currently, if a process' parent called hsaKmtOpen, the child will be
unable to open a connection to KFD, since kfd_open_count will be > 0.

When forking, the refcount should be reset, in order to allow the child
to re-open /dev/kfd.

Change-Id: Ia4b78f6bacc4f82e8ac724e5f488a3eff5084007

src/openclose.c

@@ -37,6 +37,19 @@ static const char kfd_device_name[] = "/dev/kfd";
 static const char tmp_file[] = "/var/lock/.amd_hsa_thunk_lock";
 int amd_hsa_thunk_lock_fd = 0;
 
+static bool is_forked_child(void)
+{
+	static pid_t open_pid = -1;
+	pid_t my_pid = getpid();
+
+	if (open_pid == -1 || open_pid != my_pid) {
+		open_pid = my_pid;
+		return true;
+	}
+
+	return false;
+}
+
 HSAKMT_STATUS
 HSAKMTAPI
 hsaKmtOpenKFD(void)
@@ -47,6 +60,13 @@ hsaKmtOpenKFD(void)
 
 	pthread_mutex_lock(&hsakmt_mutex);
 
+	/* If the process has forked, the child process must re-initialize
+	 * it's connection to KFD. Any references tracked by kfd_open_count
+	 * belong to the parent
+	 */
+	if (is_forked_child())
+		kfd_open_count = 0;
+
 	if (kfd_open_count == 0)
 	{
 		fd = open(kfd_device_name, O_RDWR | O_CLOEXEC);