v4.19.13 snapshot.
diff --git a/tools/testing/selftests/proc/thread-self.c b/tools/testing/selftests/proc/thread-self.c
new file mode 100644
index 0000000..4b23b39
--- /dev/null
+++ b/tools/testing/selftests/proc/thread-self.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+// Test that /proc/thread-self gives correct TGID/PID.
+#undef NDEBUG
+#include <assert.h>
+#include <sched.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+#include "proc.h"
+
+int f(void *arg)
+{
+ char buf1[64], buf2[64];
+ pid_t pid, tid;
+ ssize_t rv;
+
+ pid = sys_getpid();
+ tid = sys_gettid();
+ snprintf(buf1, sizeof(buf1), "%u/task/%u", pid, tid);
+
+ rv = readlink("/proc/thread-self", buf2, sizeof(buf2));
+ assert(rv == strlen(buf1));
+ buf2[rv] = '\0';
+ assert(streq(buf1, buf2));
+
+ if (arg)
+ exit(0);
+ return 0;
+}
+
+int main(void)
+{
+ const int PAGE_SIZE = sysconf(_SC_PAGESIZE);
+ pid_t pid;
+ void *stack;
+
+ /* main thread */
+ f((void *)0);
+
+ stack = mmap(NULL, 2 * PAGE_SIZE, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
+ assert(stack != MAP_FAILED);
+ /* side thread */
+ pid = clone(f, stack + PAGE_SIZE, CLONE_THREAD|CLONE_SIGHAND|CLONE_VM, (void *)1);
+ assert(pid > 0);
+ pause();
+
+ return 0;
+}