s390/smp: fix smp_stop_cpu() for !CONFIG_SMP

smp_stop_cpu() should stop the current cpu even for !CONFIG_SMP.
Otherwise machine_halt() will return and and the machine generates a
panic instread of simply stopping the current cpu:

Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000

CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 3.14.0-01527-g2b6ef16a6bc5 #10
[...]
Call Trace:
([<0000000000110db0>] show_trace+0xf8/0x158)
 [<0000000000110e7a>] show_stack+0x6a/0xe8
 [<000000000074dba8>] panic+0xe4/0x268
 [<0000000000140570>] do_exit+0xa88/0xb2c
 [<000000000016e12c>] SyS_reboot+0x1f0/0x234
 [<000000000075da70>] sysc_nr_ok+0x22/0x28
 [<000000007d5a09b4>] 0x7d5a09b4

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/sigp.h

@@ -31,4 +31,23 @@
 #define SIGP_STATUS_INCORRECT_STATE	0x00000200UL
 #define SIGP_STATUS_NOT_RUNNING		0x00000400UL
 
+#ifndef __ASSEMBLY__
+
+static inline int __pcpu_sigp(u16 addr, u8 order, u32 parm, u32 *status)
+{
+	register unsigned int reg1 asm ("1") = parm;
+	int cc;
+
+	asm volatile(
+		"	sigp	%1,%2,0(%3)\n"
+		"	ipm	%0\n"
+		"	srl	%0,28\n"
+		: "=d" (cc), "+d" (reg1) : "d" (addr), "a" (order) : "cc");
+	if (status && cc == 1)
+		*status = reg1;
+	return cc;
+}
+
+#endif /* __ASSEMBLY__ */
+
 #endif /* __S390_ASM_SIGP_H */

arch/s390/include/asm/smp.h

@@ -7,6 +7,8 @@
 #ifndef __ASM_SMP_H
 #define __ASM_SMP_H
 
+#include <asm/sigp.h>
+
 #ifdef CONFIG_SMP
 
 #include <asm/lowcore.h>
@@ -50,9 +52,18 @@ static inline int smp_store_status(int cpu) { return 0; }
 static inline int smp_vcpu_scheduled(int cpu) { return 1; }
 static inline void smp_yield_cpu(int cpu) { }
 static inline void smp_yield(void) { }
-static inline void smp_stop_cpu(void) { }
 static inline void smp_fill_possible_mask(void) { }
 
+static inline void smp_stop_cpu(void)
+{
+	u16 pcpu = stap();
+
+	for (;;) {
+		__pcpu_sigp(pcpu, SIGP_STOP, 0, NULL);
+		cpu_relax();
+	}
+}
+
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_HOTPLUG_CPU

arch/s390/kernel/smp.c

@@ -82,21 +82,6 @@ DEFINE_MUTEX(smp_cpu_state_mutex);
 /*
  * Signal processor helper functions.
  */
-static inline int __pcpu_sigp(u16 addr, u8 order, u32 parm, u32 *status)
-{
-	register unsigned int reg1 asm ("1") = parm;
-	int cc;
-
-	asm volatile(
-		"	sigp	%1,%2,0(%3)\n"
-		"	ipm	%0\n"
-		"	srl	%0,28\n"
-		: "=d" (cc), "+d" (reg1) : "d" (addr), "a" (order) : "cc");
-	if (status && cc == 1)
-		*status = reg1;
-	return cc;
-}
-
 static inline int __pcpu_sigp_relax(u16 addr, u8 order, u32 parm, u32 *status)
 {
 	int cc;