s390/ftrace: fix potential crashes when switching tracers

Switching tracers include instruction patching. To prevent that a
instruction is patched while it's read the instruction patching is done
in stop_machine 'context'. This also means that any function called
during stop_machine must not be traced. Thus add 'notrace' to all
functions called within stop_machine.

Fixes: 1ec2772e ("s390/diag: add a statistic for diagnose calls")
Fixes: 38f2c691 ("s390: improve wait logic of stop_machine")
Fixes: 4ecf0a43 ("processor: get rid of cpu_relax_yield")
Signed-off-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/kernel/diag.c

@@ -133,7 +133,7 @@ void diag_stat_inc(enum diag_stat_enum nr)
 }
 EXPORT_SYMBOL(diag_stat_inc);
 
-void diag_stat_inc_norecursion(enum diag_stat_enum nr)
+void notrace diag_stat_inc_norecursion(enum diag_stat_enum nr)
 {
 	this_cpu_inc(diag_stat.counter[nr]);
 	trace_s390_diagnose_norecursion(diag_map[nr].code);

arch/s390/kernel/smp.c

@@ -403,7 +403,7 @@ int smp_find_processor_id(u16 address)
 	return -1;
 }
 
-bool arch_vcpu_is_preempted(int cpu)
+bool notrace arch_vcpu_is_preempted(int cpu)
 {
 	if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu))
 		return false;
@@ -413,7 +413,7 @@ bool arch_vcpu_is_preempted(int cpu)
 }
 EXPORT_SYMBOL(arch_vcpu_is_preempted);
 
-void smp_yield_cpu(int cpu)
+void notrace smp_yield_cpu(int cpu)
 {
 	if (!MACHINE_HAS_DIAG9C)
 		return;

arch/s390/kernel/trace.c

@@ -14,7 +14,7 @@ EXPORT_TRACEPOINT_SYMBOL(s390_diagnose);
 
 static DEFINE_PER_CPU(unsigned int, diagnose_trace_depth);
 
-void trace_s390_diagnose_norecursion(int diag_nr)
+void notrace trace_s390_diagnose_norecursion(int diag_nr)
 {
 	unsigned long flags;
 	unsigned int *depth;