selftests/x86/ptrace_syscall: Fix for yet more glibc interference

glibc keeps getting cleverer, and my version now turns raise() into
more than one syscall.  Since the test relies on ptrace seeing an
exact set of syscalls, this breaks the test.  Replace raise(SIGSTOP)
with syscall(SYS_tgkill, ...) to force glibc to get out of our way.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kselftest@vger.kernel.org
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/bc80338b453afa187bc5f895bd8e2c8d6e264da2.1521300271.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/tools/testing/selftests/x86/ptrace_syscall.c b/tools/testing/selftests/x86/ptrace_syscall.c
index 1ae1c5a..6f22238 100644
--- a/tools/testing/selftests/x86/ptrace_syscall.c
+++ b/tools/testing/selftests/x86/ptrace_syscall.c
@@ -183,8 +183,10 @@
 		if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0)
 			err(1, "PTRACE_TRACEME");
 
+		pid_t pid = getpid(), tid = syscall(SYS_gettid);
+
 		printf("\tChild will make one syscall\n");
-		raise(SIGSTOP);
+		syscall(SYS_tgkill, pid, tid, SIGSTOP);
 
 		syscall(SYS_gettid, 10, 11, 12, 13, 14, 15);
 		_exit(0);
@@ -301,9 +303,11 @@
 		if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0)
 			err(1, "PTRACE_TRACEME");
 
+		pid_t pid = getpid(), tid = syscall(SYS_gettid);
+
 		printf("\tChild will take a nap until signaled\n");
 		setsigign(SIGUSR1, SA_RESTART);
-		raise(SIGSTOP);
+		syscall(SYS_tgkill, pid, tid, SIGSTOP);
 
 		syscall(SYS_pause, 0, 0, 0, 0, 0, 0);
 		_exit(0);