[PATCH v1 2/4] powerpc/ftrace: Add recursion protection in prepare_ftrace_return()

[Christophe Leroy]

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.

Reported-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
Fixes: 830213786c49 ("powerpc/ftrace: directly call of function graph tracer by 
ftrace caller")
Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
 arch/powerpc/kernel/trace/ftrace.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/trace/ftrace.c 
b/arch/powerpc/kernel/trace/ftrace.c
index 74a176e394ef..f21b8fbd418e 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/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;
 }
-- 
2.34.1