powerpc/ftrace: Add recursion protection in prepare_ftrace_return()

The function_graph_enter() does not provide any recursion protection.

Add a protection in prepare_ftrace_return() in case
function_graph_enter() calls something that gets
function graph traced.

Fixes: 83021378 ("powerpc/ftrace: directly call of function graph tracer by ftrace caller")
Reported-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/74edf2ff0a60e66b0d9225a137100a86a0557032.1644949750.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/trace/ftrace.c

@@ -944,6 +944,7 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
 						unsigned long sp)
 {
 	unsigned long return_hooker;
+	int bit;
 
 	if (unlikely(ftrace_graph_is_dead()))
 		goto out;
@@ -951,10 +952,16 @@ unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip,
 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		goto out;
 
+	bit = ftrace_test_recursion_trylock(ip, parent);
+	if (bit < 0)
+		goto out;
+
 	return_hooker = ppc_function_entry(return_to_handler);
 
 	if (!function_graph_enter(parent, ip, 0, (unsigned long *)sp))
 		parent = return_hooker;
+
+	ftrace_test_recursion_unlock(bit);
 out:
 	return parent;
 }