diff --git a/arch/s390/include/asm/unwind.h b/arch/s390/include/asm/unwind.h
index d827b5b9a32c..eaaefeceef6f 100644
--- a/arch/s390/include/asm/unwind.h
+++ b/arch/s390/include/asm/unwind.h
@@ -35,6 +35,7 @@ struct unwind_state {
 	struct task_struct *task;
 	struct pt_regs *regs;
 	unsigned long sp, ip;
+	bool reuse_sp;
 	int graph_idx;
 	bool reliable;
 	bool error;
diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
index b9d8fe45737a..8f8456816d83 100644
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -69,18 +69,26 @@ DEVICE_ATTR(idle_count, 0444, show_idle_count, NULL);
 static ssize_t show_idle_time(struct device *dev,
 				struct device_attribute *attr, char *buf)
 {
+	unsigned long long now, idle_time, idle_enter, idle_exit, in_idle;
 	struct s390_idle_data *idle = &per_cpu(s390_idle, dev->id);
-	unsigned long long now, idle_time, idle_enter, idle_exit;
 	unsigned int seq;
 
 	do {
-		now = get_tod_clock();
 		seq = read_seqcount_begin(&idle->seqcount);
 		idle_time = READ_ONCE(idle->idle_time);
 		idle_enter = READ_ONCE(idle->clock_idle_enter);
 		idle_exit = READ_ONCE(idle->clock_idle_exit);
 	} while (read_seqcount_retry(&idle->seqcount, seq));
-	idle_time += idle_enter ? ((idle_exit ? : now) - idle_enter) : 0;
+	in_idle = 0;
+	now = get_tod_clock();
+	if (idle_enter) {
+		if (idle_exit) {
+			in_idle = idle_exit - idle_enter;
+		} else if (now > idle_enter) {
+			in_idle = now - idle_enter;
+		}
+	}
+	idle_time += in_idle;
 	return sprintf(buf, "%llu\n", idle_time >> 12);
 }
 DEVICE_ATTR(idle_time_us, 0444, show_idle_time, NULL);
@@ -88,17 +96,24 @@ DEVICE_ATTR(idle_time_us, 0444, show_idle_time, NULL);
 u64 arch_cpu_idle_time(int cpu)
 {
 	struct s390_idle_data *idle = &per_cpu(s390_idle, cpu);
-	unsigned long long now, idle_enter, idle_exit;
+	unsigned long long now, idle_enter, idle_exit, in_idle;
 	unsigned int seq;
 
 	do {
-		now = get_tod_clock();
 		seq = read_seqcount_begin(&idle->seqcount);
 		idle_enter = READ_ONCE(idle->clock_idle_enter);
 		idle_exit = READ_ONCE(idle->clock_idle_exit);
 	} while (read_seqcount_retry(&idle->seqcount, seq));
-
-	return cputime_to_nsecs(idle_enter ? ((idle_exit ?: now) - idle_enter) : 0);
+	in_idle = 0;
+	now = get_tod_clock();
+	if (idle_enter) {
+		if (idle_exit) {
+			in_idle = idle_exit - idle_enter;
+		} else if (now > idle_enter) {
+			in_idle = now - idle_enter;
+		}
+	}
+	return cputime_to_nsecs(in_idle);
 }
 
 void arch_cpu_idle_enter(void)
diff --git a/arch/s390/kernel/unwind_bc.c b/arch/s390/kernel/unwind_bc.c
index 8fc9daae47a2..a8204f952315 100644
--- a/arch/s390/kernel/unwind_bc.c
+++ b/arch/s390/kernel/unwind_bc.c
@@ -46,10 +46,15 @@ bool unwind_next_frame(struct unwind_state *state)
 
 	regs = state->regs;
 	if (unlikely(regs)) {
-		sp = READ_ONCE_NOCHECK(regs->gprs[15]);
-		if (unlikely(outside_of_stack(state, sp))) {
-			if (!update_stack_info(state, sp))
-				goto out_err;
+		if (state->reuse_sp) {
+			sp = state->sp;
+			state->reuse_sp = false;
+		} else {
+			sp = READ_ONCE_NOCHECK(regs->gprs[15]);
+			if (unlikely(outside_of_stack(state, sp))) {
+				if (!update_stack_info(state, sp))
+					goto out_err;
+			}
 		}
 		sf = (struct stack_frame *) sp;
 		ip = READ_ONCE_NOCHECK(sf->gprs[8]);
@@ -107,9 +112,9 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 {
 	struct stack_info *info = &state->stack_info;
 	unsigned long *mask = &state->stack_mask;
+	bool reliable, reuse_sp;
 	struct stack_frame *sf;
 	unsigned long ip;
-	bool reliable;
 
 	memset(state, 0, sizeof(*state));
 	state->task = task;
@@ -134,10 +139,12 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 	if (regs) {
 		ip = READ_ONCE_NOCHECK(regs->psw.addr);
 		reliable = true;
+		reuse_sp = true;
 	} else {
 		sf = (struct stack_frame *) sp;
 		ip = READ_ONCE_NOCHECK(sf->gprs[8]);
 		reliable = false;
+		reuse_sp = false;
 	}
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -151,5 +158,6 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 	state->sp = sp;
 	state->ip = ip;
 	state->reliable = reliable;
+	state->reuse_sp = reuse_sp;
 }
 EXPORT_SYMBOL_GPL(__unwind_start);
diff --git a/arch/s390/mm/cmm.c b/arch/s390/mm/cmm.c
index 510a18299196..a51c892f14f3 100644
--- a/arch/s390/mm/cmm.c
+++ b/arch/s390/mm/cmm.c
@@ -298,16 +298,16 @@ static int cmm_timeout_handler(struct ctl_table *ctl, int write,
 	}
 
 	if (write) {
-		len = *lenp;
-		if (copy_from_user(buf, buffer,
-				   len > sizeof(buf) ? sizeof(buf) : len))
+		len = min(*lenp, sizeof(buf));
+		if (copy_from_user(buf, buffer, len))
 			return -EFAULT;
-		buf[sizeof(buf) - 1] = '\0';
+		buf[len - 1] = '\0';
 		cmm_skip_blanks(buf, &p);
 		nr = simple_strtoul(p, &p, 0);
 		cmm_skip_blanks(p, &p);
 		seconds = simple_strtoul(p, &p, 0);
 		cmm_set_timeout(nr, seconds);
+		*ppos += *lenp;
 	} else {
 		len = sprintf(buf, "%ld %ld\n",
 			      cmm_timeout_pages, cmm_timeout_seconds);
@@ -315,9 +315,9 @@ static int cmm_timeout_handler(struct ctl_table *ctl, int write,
 			len = *lenp;
 		if (copy_to_user(buffer, buf, len))
 			return -EFAULT;
+		*lenp = len;
+		*ppos += len;
 	}
-	*lenp = len;
-	*ppos += len;
 	return 0;
 }