s390: remove dead code from signal handler

The code in entry[64].S calls do_signal only on return to user space.
user_mode(regs) is true for every calls to do_signal, it is unnecessary
to recheck user_mode at the start of do_signal and the legacy signal
stack switching path in get_sigframe is never reached.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/compat_signal.c

@@ -437,13 +437,6 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs * regs, size_t frame_size)
 			sp = current->sas_ss_sp + current->sas_ss_size;
 	}
 
-	/* This is the legacy signal stack switching. */
-	else if (!user_mode(regs) &&
-		 !(ka->sa.sa_flags & SA_RESTORER) &&
-		 ka->sa.sa_restorer) {
-		sp = (unsigned long) ka->sa.sa_restorer;
-	}
-
 	return (void __user *)((sp - frame_size) & -8ul);
 }
 

arch/s390/kernel/signal.c

@@ -235,13 +235,6 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs * regs, size_t frame_size)
 			sp = current->sas_ss_sp + current->sas_ss_size;
 	}
 
-	/* This is the legacy signal stack switching. */
-	else if (!user_mode(regs) &&
-		 !(ka->sa.sa_flags & SA_RESTORER) &&
-		 ka->sa.sa_restorer) {
-		sp = (unsigned long) ka->sa.sa_restorer;
-	}
-
 	return (void __user *)((sp - frame_size) & -8ul);
 }
 
@@ -414,15 +407,6 @@ void do_signal(struct pt_regs *regs)
 	struct k_sigaction ka;
 	sigset_t *oldset;
 
-	/*
-	 * We want the common case to go fast, which
-	 * is why we may in certain cases get here from
-	 * kernel mode. Just return without doing anything
-	 * if so.
-	 */
-	if (!user_mode(regs))
-		return;
-
 	if (test_thread_flag(TIF_RESTORE_SIGMASK))
 		oldset = &current->saved_sigmask;
 	else