s390/ptrace: pass invalid syscall numbers to tracing

tracing expects to see invalid syscalls, so pass it through.
The syscall path in entry.S checks the syscall number before
looking up the handler, so it is still safe.
Signed-off-by: NSven Schnelle <svens@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/entry.S

@@ -401,9 +401,9 @@ ENTRY(system_call)
 	jnz	.Lsysc_nr_ok
 	# svc 0: system call number in %r1
 	llgfr	%r1,%r1				# clear high word in r1
+	sth	%r1,__PT_INT_CODE+2(%r11)
 	cghi	%r1,NR_syscalls
 	jnl	.Lsysc_nr_ok
-	sth	%r1,__PT_INT_CODE+2(%r11)
 	slag	%r8,%r1,3
 .Lsysc_nr_ok:
 	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)

arch/s390/kernel/ptrace.c

@@ -847,11 +847,9 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
 	 * call number to gprs[2].
 	 */
 	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
-	    (tracehook_report_syscall_entry(regs) ||
-	     regs->gprs[2] >= NR_syscalls)) {
+	    tracehook_report_syscall_entry(regs)) {
 		/*
-		 * Tracing decided this syscall should not happen or the
-		 * debugger stored an invalid system call number. Skip
+		 * Tracing decided this syscall should not happen. Skip
 		 * the system call and the system call restart handling.
 		 */
 		goto skip;