[S390] kprobes: defer setting of ctlblk state

get_krobe_ctlblk returns a per cpu kprobe control block which holds
the state of the current cpu wrt to kprobe.
When inserting/removing a kprobe the state of the cpu which replaces
the code is changed to KPROBE_SWAP_INST. This however is done when
preemption is still enabled. So the state of the current cpu doesn't
necessarily reflect the real state.
To fix this move the code that changes the state to non-preemptible
context.
Reported-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/kprobes.c

@@ -154,39 +154,35 @@ void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
 
 static int __kprobes swap_instruction(void *aref)
 {
+	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long status = kcb->kprobe_status;
 	struct ins_replace_args *args = aref;
+	int rc;
 
-	return probe_kernel_write(args->ptr, &args->new, sizeof(args->new));
+	kcb->kprobe_status = KPROBE_SWAP_INST;
+	rc = probe_kernel_write(args->ptr, &args->new, sizeof(args->new));
+	kcb->kprobe_status = status;
+	return rc;
 }
 
 void __kprobes arch_arm_kprobe(struct kprobe *p)
 {
-	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
-	unsigned long status = kcb->kprobe_status;
 	struct ins_replace_args args;
 
 	args.ptr = p->addr;
 	args.old = p->opcode;
 	args.new = BREAKPOINT_INSTRUCTION;
-
-	kcb->kprobe_status = KPROBE_SWAP_INST;
 	stop_machine(swap_instruction, &args, NULL);
-	kcb->kprobe_status = status;
 }
 
 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 {
-	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
-	unsigned long status = kcb->kprobe_status;
 	struct ins_replace_args args;
 
 	args.ptr = p->addr;
 	args.old = BREAKPOINT_INSTRUCTION;
 	args.new = p->opcode;
-
-	kcb->kprobe_status = KPROBE_SWAP_INST;
 	stop_machine(swap_instruction, &args, NULL);
-	kcb->kprobe_status = status;
 }
 
 void __kprobes arch_remove_kprobe(struct kprobe *p)