2 files changed, 40 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3e7bf5eb9007..d576dbd6defe 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -244,6 +244,7 @@ static const char *trace_options[] = {
         "stacktrace",
         "sched-tree",
         "ftrace_printk",
+        "ftrace_preempt",
         NULL
 };
 
@@ -891,7 +892,7 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3)
 
 #ifdef CONFIG_FUNCTION_TRACER
 static void
-function_trace_call(unsigned long ip, unsigned long parent_ip)
+function_trace_call_preempt_only(unsigned long ip, unsigned long parent_ip)
 {
         struct trace_array *tr = &global_trace;
         struct trace_array_cpu *data;
@@ -917,6 +918,37 @@ function_trace_call(unsigned long ip, unsigned long parent_ip)
         ftrace_preempt_enable(resched);
 }
 
+static void
+function_trace_call(unsigned long ip, unsigned long parent_ip)
+{
+        struct trace_array *tr = &global_trace;
+        struct trace_array_cpu *data;
+        unsigned long flags;
+        long disabled;
+        int cpu;
+        int pc;
+
+        if (unlikely(!ftrace_function_enabled))
+                return;
+
+        /*
+         * Need to use raw, since this must be called before the
+         * recursive protection is performed.
+         */
+        raw_local_irq_save(flags);
+        cpu = raw_smp_processor_id();
+        data = tr->data[cpu];
+        disabled = atomic_inc_return(&data->disabled);
+
+        if (likely(disabled == 1)) {
+                pc = preempt_count();
+                trace_function(tr, data, ip, parent_ip, flags, pc);
+        }
+
+        atomic_dec(&data->disabled);
+        raw_local_irq_restore(flags);
+}
+
 static struct ftrace_ops trace_ops __read_mostly =
 {
         .func = function_trace_call,
@@ -925,6 +957,12 @@ static struct ftrace_ops trace_ops __read_mostly =
 void tracing_start_function_trace(void)
 {
         ftrace_function_enabled = 0;
+
+        if (trace_flags & TRACE_ITER_PREEMPTONLY)
+                trace_ops.func = function_trace_call_preempt_only;
+        else
+                trace_ops.func = function_trace_call;
+
         register_ftrace_function(&trace_ops);
         if (tracer_enabled)
                 ftrace_function_enabled = 1;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 10c6dae76894..bb547e933af7 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -415,6 +415,7 @@ enum trace_iterator_flags {
         TRACE_ITER_STACKTRACE           = 0x100,
         TRACE_ITER_SCHED_TREE           = 0x200,
         TRACE_ITER_PRINTK               = 0x400,
+        TRACE_ITER_PREEMPTONLY          = 0x800,
 };
 
 extern struct tracer nop_trace;