ftrace: function graph return for function entry

Impact: feature, let entry function decide to trace or not

This patch lets the graph tracer entry function decide if the tracing
should be done at the end as well. This requires all function graph
entry functions return 1 if it should trace, or 0 if the return should
not be traced.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 12 insertions, 1 deletions

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 826682abed1d..43ceb3f454bf 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1196,6 +1196,9 @@ ENTRY(mcount)
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
         cmpl $ftrace_stub, ftrace_graph_return
         jnz ftrace_graph_caller
+
+        cmpl $ftrace_graph_entry_stub, ftrace_graph_entry
+        jnz ftrace_graph_caller
 #endif
 .globl ftrace_stub
 ftrace_stub:
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 9060ba6497e2..54e0bbdccb99 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -120,6 +120,9 @@ ENTRY(mcount)
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
         cmpq $ftrace_stub, ftrace_graph_return
         jnz ftrace_graph_caller
+
+        cmpq $ftrace_graph_entry_stub, ftrace_graph_entry
+        jnz ftrace_graph_caller
 #endif
 
 .globl ftrace_stub
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index adba8e9a427c..d278ad2ebda2 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -425,6 +425,7 @@ static void pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret)
         trace->calltime = current->ret_stack[index].calltime;
         trace->overrun = atomic_read(&current->trace_overrun);
         trace->depth = index;
+        barrier();
         current->curr_ret_stack--;
 }
 
@@ -506,7 +507,11 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
         }
 
         trace.func = self_addr;
-        ftrace_graph_entry(&trace);
 
+        /* Only trace if the calling function expects to */
+        if (!ftrace_graph_entry(&trace)) {
+                current->curr_ret_stack--;
+                *parent = old;
+        }
 }
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */