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Subject[PATCH 5/7] ftrace, perf: Add support to use function tracepoint in perf
Date
Adding perf registration support for the ftrace function event,
so it is now possible to register it via perf interface.

The perf_event struct statically contains ftrace_ops as a handle
for function tracer. The function tracer is registered/unregistered
in open/close actions.

To be efficient, we enable/disable ftrace_ops each time the traced
process is scheduled in/out (via TRACE_REG_PERF_(ADD|DELL) handlers).
This way tracing is enabled only when the process is running.
Intentionally using this way instead of the event's hw state
PERF_HES_STOPPED, which would not disable the ftrace_ops.
It is now possible to use function trace within perf commands
like:

perf record -e ftrace:function ls
perf stat -e ftrace:function ls

Allowed only for root.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
include/linux/perf_event.h | 3 +
kernel/trace/trace.h | 2 +
kernel/trace/trace_event_perf.c | 92 +++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_export.c | 28 ++++++++++++
4 files changed, 125 insertions(+), 0 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 0b91db2..5003be6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -858,6 +858,9 @@ struct perf_event {
#ifdef CONFIG_EVENT_TRACING
struct ftrace_event_call *tp_event;
struct event_filter *filter;
+#ifdef CONFIG_FUNCTION_TRACER
+ struct ftrace_ops ftrace_ops;
+#endif
#endif

#ifdef CONFIG_CGROUP_PERF
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 85732a8..e88e58a 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -591,6 +591,8 @@ static inline int ftrace_trace_task(struct task_struct *task)
static inline int ftrace_is_dead(void) { return 0; }
#endif

+int ftrace_event_is_function(struct ftrace_event_call *call);
+
/*
* struct trace_parser - servers for reading the user input separated by spaces
* @cont: set if the input is not complete - no final space char was found
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index d72af0b..57eb232 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -24,6 +24,11 @@ static int total_ref_count;
static int perf_trace_event_perm(struct ftrace_event_call *tp_event,
struct perf_event *p_event)
{
+ /* The ftrace function trace is allowed only for root. */
+ if (ftrace_event_is_function(tp_event) &&
+ perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
/* No tracing, just counting, so no obvious leak */
if (!(p_event->attr.sample_type & PERF_SAMPLE_RAW))
return 0;
@@ -250,3 +255,90 @@ __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
return raw_data;
}
EXPORT_SYMBOL_GPL(perf_trace_buf_prepare);
+
+
+static void
+perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip)
+{
+ struct ftrace_entry *entry;
+ struct hlist_head *head;
+ struct pt_regs regs;
+ int rctx;
+
+#define ENTRY_SIZE (ALIGN(sizeof(struct ftrace_entry) + sizeof(u32), \
+ sizeof(u64)) - sizeof(u32))
+
+ BUILD_BUG_ON(ENTRY_SIZE > PERF_MAX_TRACE_SIZE);
+
+ perf_fetch_caller_regs(&regs);
+
+ entry = perf_trace_buf_prepare(ENTRY_SIZE, TRACE_FN, NULL, &rctx);
+ if (!entry)
+ return;
+
+ entry->ip = ip;
+ entry->parent_ip = parent_ip;
+
+ head = this_cpu_ptr(event_function.perf_events);
+ perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, 0,
+ 1, &regs, head);
+
+#undef ENTRY_SIZE
+}
+
+static int perf_ftrace_function_register(struct perf_event *event)
+{
+ struct ftrace_ops *ops = &event->ftrace_ops;
+
+ ops->flags |= FTRACE_OPS_FL_CONTROL;
+ ops->func = perf_ftrace_function_call;
+ return register_ftrace_function(ops);
+}
+
+static int perf_ftrace_function_unregister(struct perf_event *event)
+{
+ struct ftrace_ops *ops = &event->ftrace_ops;
+ return unregister_ftrace_function(ops);
+}
+
+static void perf_ftrace_function_enable(struct perf_event *event)
+{
+ struct ftrace_ops *ops = &event->ftrace_ops;
+ ftrace_function_enable(ops, smp_processor_id());
+}
+
+static void perf_ftrace_function_disable(struct perf_event *event)
+{
+ struct ftrace_ops *ops = &event->ftrace_ops;
+ ftrace_function_disable(ops, smp_processor_id());
+}
+
+int perf_ftrace_event_register(struct ftrace_event_call *call,
+ enum trace_reg type, void *data)
+{
+ int etype = call->event.type;
+
+ if (etype != TRACE_FN)
+ return -EINVAL;
+
+ switch (type) {
+ case TRACE_REG_REGISTER:
+ case TRACE_REG_UNREGISTER:
+ break;
+ case TRACE_REG_PERF_REGISTER:
+ case TRACE_REG_PERF_UNREGISTER:
+ return 0;
+ case TRACE_REG_PERF_OPEN:
+ return perf_ftrace_function_register(data);
+ case TRACE_REG_PERF_CLOSE:
+ return perf_ftrace_function_unregister(data);
+ case TRACE_REG_PERF_ADD:
+ perf_ftrace_function_enable(data);
+ return 0;
+ case TRACE_REG_PERF_DEL:
+ perf_ftrace_function_disable(data);
+ return 0;
+ }
+
+ return -EINVAL;
+}
diff --git a/kernel/trace/trace_export.c b/kernel/trace/trace_export.c
index bbeec31..867653c 100644
--- a/kernel/trace/trace_export.c
+++ b/kernel/trace/trace_export.c
@@ -131,6 +131,28 @@ ftrace_define_fields_##name(struct ftrace_event_call *event_call) \

#include "trace_entries.h"

+static int ftrace_event_class_register(struct ftrace_event_call *call,
+ enum trace_reg type, void *data)
+{
+ switch (type) {
+ case TRACE_REG_PERF_REGISTER:
+ case TRACE_REG_PERF_UNREGISTER:
+ return 0;
+ case TRACE_REG_PERF_OPEN:
+ case TRACE_REG_PERF_CLOSE:
+ case TRACE_REG_PERF_ADD:
+ case TRACE_REG_PERF_DEL:
+#ifdef CONFIG_PERF_EVENTS
+ return perf_ftrace_event_register(call, type, data);
+#endif
+ case TRACE_REG_REGISTER:
+ case TRACE_REG_UNREGISTER:
+ break;
+ }
+
+ return -EINVAL;
+}
+
#undef __entry
#define __entry REC

@@ -159,6 +181,7 @@ struct ftrace_event_class event_class_ftrace_##call = { \
.system = __stringify(TRACE_SYSTEM), \
.define_fields = ftrace_define_fields_##call, \
.fields = LIST_HEAD_INIT(event_class_ftrace_##call.fields),\
+ .reg = ftrace_event_class_register, \
}; \
\
struct ftrace_event_call __used event_##call = { \
@@ -170,4 +193,9 @@ struct ftrace_event_call __used event_##call = { \
struct ftrace_event_call __used \
__attribute__((section("_ftrace_events"))) *__event_##call = &event_##call;

+int ftrace_event_is_function(struct ftrace_event_call *call)
+{
+ return call == &event_function;
+}
+
#include "trace_entries.h"
--
1.7.1


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