s390/ftrace: add ftrace_graph_is_dead() check

Add an ftrace_graph_is_dead() check to prepare_ftrace_return() in order to
detect an internal ftrace graph error. This allows to prevent further ftrace
graph handling and hopefully keeps the kernel alive.

This patch is the same like for all other architectures.
For unkown reasons s390 was left out.
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/ftrace.c

@@ -121,6 +121,8 @@ unsigned long __kprobes prepare_ftrace_return(unsigned long parent,
 {
 	struct ftrace_graph_ent trace;
 
+	if (unlikely(ftrace_graph_is_dead()))
+		goto out;
 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		goto out;
 	ip = (ip & PSW_ADDR_INSN) - MCOUNT_INSN_SIZE;