sh: Fix restartable syscall arg5 clobbering.

We use R0 as the 5th argument of syscall.  When the syscall restarts
after signal handling, we should restore the old value of R0.
The attached patch does it. Without this patch, I've experienced random
failures in the situation which signals are issued frequently.
Signed-off-by: NKaz Kojima <kkojima@rr.iij4u.or.jp>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/kernel/signal.c

@@ -481,7 +481,7 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 
 static int
 handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
-	      sigset_t *oldset, struct pt_regs *regs)
+	      sigset_t *oldset, struct pt_regs *regs, unsigned int save_r0)
 {
 	int ret;
 
@@ -500,6 +500,7 @@ handle_signal(unsigned long sig, struct k_sigaction *ka, siginfo_t *info,
 				}
 			/* fallthrough */
 			case -ERESTARTNOINTR:
+				regs->regs[0] = save_r0;
 				regs->pc -= instruction_size(
 						ctrl_inw(regs->pc - 4));
 				break;
@@ -583,7 +584,8 @@ static void do_signal(struct pt_regs *regs, unsigned int save_r0)
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 	if (signr > 0) {
 		/* Whee!  Actually deliver the signal.  */
-		if (handle_signal(signr, &ka, &info, oldset, regs) == 0) {
+		if (handle_signal(signr, &ka, &info, oldset, regs, save_r0)
+		    == 0) {
 			/* a signal was successfully delivered; the saved
 			 * sigmask will have been stored in the signal frame,
 			 * and will be restored by sigreturn, so we can simply