[PATCH 01/20 v2] tracing: Add function based events

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

Add an interface that hooks to the ftrace function tracing to create events
based on functions. A new file is created in the tracefs file system called
function_events. Writing a function name followed by an empty set of
parenthesis will create an event that uses ftrace function callbacks to
record the data. Currently the function takes no arguments, but that will
soon change. The next step is to have arguments within those parenthesis,
and an event created to show it.

Thanks to Jiri Olsa for pointing out the missing mutex protection in
create_function_event().

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 include/linux/trace_events.h      |   2 +
 kernel/trace/Kconfig              |  12 +
 kernel/trace/Makefile             |   1 +
 kernel/trace/trace.h              |  11 +
 kernel/trace/trace_event_ftrace.c | 473 ++++++++++++++++++++++++++++++++++++++
 kernel/trace/trace_probe.h        |  11 -
 6 files changed, 499 insertions(+), 11 deletions(-)
 create mode 100644 kernel/trace/trace_event_ftrace.c

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index af44e7c2d577..6a3600009c48 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -226,6 +226,7 @@ enum {
 	TRACE_EVENT_FL_TRACEPOINT_BIT,
 	TRACE_EVENT_FL_KPROBE_BIT,
 	TRACE_EVENT_FL_UPROBE_BIT,
+	TRACE_EVENT_FL_FUNC_BIT,
 };
 
 /*
@@ -246,6 +247,7 @@ enum {
 	TRACE_EVENT_FL_TRACEPOINT	= (1 << TRACE_EVENT_FL_TRACEPOINT_BIT),
 	TRACE_EVENT_FL_KPROBE		= (1 << TRACE_EVENT_FL_KPROBE_BIT),
 	TRACE_EVENT_FL_UPROBE		= (1 << TRACE_EVENT_FL_UPROBE_BIT),
+	TRACE_EVENT_FL_FUNC		= (1 << TRACE_EVENT_FL_FUNC_BIT),
 };
 
 #define TRACE_EVENT_FL_UKPROBE (TRACE_EVENT_FL_KPROBE | TRACE_EVENT_FL_UPROBE)
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index f54dc62b599c..2118838946cd 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -442,6 +442,18 @@ config BLK_DEV_IO_TRACE
 
 	  If unsure, say N.
 
+config FUNCTION_EVENTS
+	depends on DYNAMIC_FTRACE_WITH_REGS
+	bool "Enable function based events"
+	select TRACING
+	help
+	 This creates a file function_events in the tracefs file system.
+	 Writing function names into this file will create an event
+	 that can be enabled like any other event, but will be at the
+	 location of the specified function.
+
+	 See Documentation/trace/function_events.txt for more details.
+
 config KPROBE_EVENTS
 	depends on KPROBES
 	depends on HAVE_REGS_AND_STACK_ACCESS_API
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index e2538c7638d4..00f6d69652c0 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -55,6 +55,7 @@ obj-$(CONFIG_FTRACE_SYSCALLS) += trace_syscalls.o
 ifeq ($(CONFIG_PERF_EVENTS),y)
 obj-$(CONFIG_EVENT_TRACING) += trace_event_perf.o
 endif
+obj-$(CONFIG_FUNCTION_EVENTS) += trace_event_ftrace.o
 obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
 obj-$(CONFIG_HIST_TRIGGERS) += trace_events_hist.o
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 2a6d0325a761..67928b53dc06 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1814,4 +1814,15 @@ static inline void trace_event_eval_update(struct trace_eval_map **map, int len)
 
 extern struct trace_iterator *tracepoint_print_iter;
 
+#undef DEFINE_FIELD
+#define DEFINE_FIELD(type, item, name, is_signed)			\
+	do {								\
+		ret = trace_define_field(event_call, #type, name,	\
+					 offsetof(typeof(field), item),	\
+					 sizeof(field.item), is_signed, \
+					 FILTER_OTHER);			\
+		if (ret)						\
+			return ret;					\
+	} while (0)
+
 #endif /* _LINUX_KERNEL_TRACE_H */
diff --git a/kernel/trace/trace_event_ftrace.c b/kernel/trace/trace_event_ftrace.c
new file mode 100644
index 000000000000..fb8e03e663e8
--- /dev/null
+++ b/kernel/trace/trace_event_ftrace.c
@@ -0,0 +1,473 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * trace events created on top of ftrace (functions).
+ *
+ * Copyright (C) 2018 VMware Inc, Steven Rostedt.
+ */
+
+#include <linux/ctype.h>
+#include <linux/slab.h>
+
+#include "trace.h"
+
+#define FUNC_EVENT_SYSTEM "functions"
+#define WRITE_BUFSIZE  4096
+
+struct func_event {
+	struct list_head		list;
+	char				*func;
+	struct trace_event_class	class;
+	struct trace_event_call		call;
+	struct ftrace_ops		ops;
+	struct list_head		files;
+};
+
+struct func_file {
+	struct list_head		list;
+	struct trace_event_file		*file;
+};
+
+struct func_event_hdr {
+	struct trace_entry	ent;
+	unsigned long		ip;
+	unsigned long		parent_ip;
+};
+
+static DEFINE_MUTEX(func_event_mutex);
+static LIST_HEAD(func_events);
+
+enum func_states {
+	FUNC_STATE_INIT,
+	FUNC_STATE_FUNC,
+	FUNC_STATE_PARAM,
+	FUNC_STATE_END,
+	FUNC_STATE_ERROR,
+};
+
+static void free_func_event(struct func_event *func_event)
+{
+	if (!func_event)
+		return;
+
+	ftrace_free_filter(&func_event->ops);
+	kfree(func_event->call.print_fmt);
+	kfree(func_event->func);
+	kfree(func_event);
+}
+
+static char *next_token(char **ptr, char *last)
+{
+	char *arg;
+	char *str;
+
+	if (!*ptr)
+		return NULL;
+
+	arg = *ptr;
+
+	if (*last)
+		*arg = *last;
+
+	if (!*arg)
+		return NULL;
+
+	for (str = arg; *str; str++) {
+		if (*str == '(' ||
+		    *str == ')')
+			break;
+	}
+	if (*str) {
+		if (str == arg)
+			str++;
+		*last = *str;
+		*str = 0;
+		*ptr = str;
+		return arg;
+	}
+
+	*last = 0;
+	*ptr = NULL;
+	return arg;
+}
+
+static enum func_states
+process_event(struct func_event *fevent, const char *token, enum func_states state)
+{
+	switch (state) {
+	case FUNC_STATE_INIT:
+		if (!isalpha(token[0]))
+			return FUNC_STATE_ERROR;
+		/* Do not allow wild cards */
+		if (strstr(token, "*") || strstr(token, "?"))
+			return FUNC_STATE_ERROR;
+		fevent->func = kstrdup(token, GFP_KERNEL);
+		if (!fevent->func)
+			return FUNC_STATE_ERROR;
+		return FUNC_STATE_FUNC;
+
+	case FUNC_STATE_FUNC:
+		if (token[0] != '(')
+			return FUNC_STATE_ERROR;
+		return FUNC_STATE_PARAM;
+
+	case FUNC_STATE_PARAM:
+		if (token[0] != ')')
+			return FUNC_STATE_ERROR;
+		return FUNC_STATE_END;
+
+	default:
+		return FUNC_STATE_ERROR;
+	}
+}
+
+static void func_event_trace(struct trace_event_file *trace_file,
+			     struct func_event *func_event,
+			     unsigned long ip, unsigned long parent_ip,
+			     struct pt_regs *pt_regs)
+{
+	struct func_event_hdr *entry;
+	struct trace_event_call *call = &func_event->call;
+	struct ring_buffer_event *event;
+	struct ring_buffer *buffer;
+	unsigned long irq_flags;
+	int size;
+	int pc;
+
+	if (trace_trigger_soft_disabled(trace_file))
+		return;
+
+	local_save_flags(irq_flags);
+	pc = preempt_count();
+
+	size = sizeof(*entry);
+
+	event = trace_event_buffer_lock_reserve(&buffer, trace_file,
+						call->event.type,
+						size, irq_flags, pc);
+	if (!event)
+		return;
+
+	entry = ring_buffer_event_data(event);
+	entry->ip = ip;
+	entry->parent_ip = parent_ip;
+
+	event_trigger_unlock_commit_regs(trace_file, buffer, event,
+					 entry, irq_flags, pc, pt_regs);
+}
+
+static void
+func_event_call(unsigned long ip, unsigned long parent_ip,
+		    struct ftrace_ops *op, struct pt_regs *pt_regs)
+{
+	struct func_event *func_event;
+	struct func_file *ff;
+
+	func_event = container_of(op, struct func_event, ops);
+
+	if (WARN_ON_ONCE(rcu_irq_enter_disabled()))
+		return;
+	rcu_irq_enter_irqson();
+	rcu_read_lock_sched_notrace();
+	list_for_each_entry_rcu(ff, &func_event->files, list) {
+		func_event_trace(ff->file, func_event, ip, parent_ip, pt_regs);
+	}
+	rcu_read_unlock_sched_notrace();
+	rcu_irq_exit_irqson();
+}
+
+
+
+static enum print_line_t
+func_event_print(struct trace_iterator *iter, int flags,
+		 struct trace_event *event)
+{
+	struct func_event_hdr *entry;
+	struct trace_seq *s = &iter->seq;
+
+	entry = (struct func_event_hdr *)iter->ent;
+
+	trace_seq_printf(s, "%ps->%ps()",
+			 (void *)entry->parent_ip, (void *)entry->ip);
+	trace_seq_putc(s, '\n');
+	return trace_handle_return(s);
+}
+
+static struct trace_event_functions func_event_funcs = {
+	.trace		= func_event_print,
+};
+
+static int func_event_define_fields(struct trace_event_call *event_call)
+{
+	struct func_event_hdr field;
+	int ret;
+
+	DEFINE_FIELD(unsigned long, ip, "__parent_ip", 0);
+	DEFINE_FIELD(unsigned long, parent_ip, "__ip", 0);
+
+	return 0;
+}
+
+static int enable_func_event(struct func_event *func_event,
+			     struct trace_event_file *file)
+{
+	struct func_file *ff;
+	int ret;
+
+	ff = kmalloc(sizeof(*ff), GFP_KERNEL);
+	if (!ff)
+		return -ENOMEM;
+
+	if (list_empty(&func_event->files)) {
+		ret = register_ftrace_function(&func_event->ops);
+		if (ret < 0)
+			return ret;
+	}
+
+	ff->file = file;
+	/* Make sure file is visible before adding to the list */
+	smp_wmb();
+	list_add_rcu(&ff->list, &func_event->files);
+	return 0;
+}
+
+static int disable_func_event(struct func_event *func_event,
+			      struct trace_event_file *file)
+{
+	struct list_head *p, *n;
+	struct func_file *ff;
+
+
+	list_for_each_safe(p, n, &func_event->files) {
+		ff = container_of(p, struct func_file, list);
+		if (ff->file == file) {
+			list_del_rcu(&ff->list);
+			break;
+		}
+		ff = NULL;
+	}
+
+	if (!ff)
+		return -ENODEV;
+
+	if (list_empty(&func_event->files))
+		unregister_ftrace_function(&func_event->ops);
+
+	synchronize_sched();
+	kfree(ff);
+
+	return 0;
+}
+
+static int func_event_register(struct trace_event_call *event,
+			       enum trace_reg type, void *data)
+{
+	struct func_event *func_event = event->data;
+	struct trace_event_file *file = data;
+
+	switch (type) {
+	case TRACE_REG_REGISTER:
+		return enable_func_event(func_event, file);
+	case TRACE_REG_UNREGISTER:
+		return disable_func_event(func_event, file);
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+static int set_print_fmt(struct func_event *func_event)
+{
+	const char *fmt = "\"%pS->%pS()\", REC->__ip, REC->__parent_ip";
+
+	func_event->call.print_fmt = kstrdup(fmt, GFP_KERNEL);
+	if (!func_event->call.print_fmt)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static int func_event_create(struct func_event *func_event)
+{
+	struct trace_event_call *call = &func_event->call;
+	int ret;
+
+	func_event->class.system = FUNC_EVENT_SYSTEM;
+	call->class = &func_event->class;
+	INIT_LIST_HEAD(&call->class->fields);
+	call->event.funcs = &func_event_funcs;
+	call->name = func_event->func;
+	call->class->define_fields = func_event_define_fields;
+	ret = set_print_fmt(func_event);
+	if (ret < 0)
+		return ret;
+	ret = register_trace_event(&call->event);
+	if (ret < 0)
+		return ret;
+	call->flags = TRACE_EVENT_FL_FUNC;
+	call->class->reg = func_event_register;
+	call->data = func_event;
+	ret = trace_add_event_call(call);
+	if (ret) {
+		pr_info("Failed to register func event: %s\n", func_event->func);
+		unregister_trace_event(&call->event);
+	}
+	return ret;
+}
+
+static int create_function_event(int argc, char **argv)
+{
+	struct func_event *func_event;
+	enum func_states state = FUNC_STATE_INIT;
+	char *token;
+	char *ptr;
+	char last;
+	int ret = -EINVAL;
+	int i;
+
+	func_event = kzalloc(sizeof(*func_event), GFP_KERNEL);
+	if (!func_event)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&func_event->files);
+	func_event->ops.func = func_event_call;
+	func_event->ops.flags = FTRACE_OPS_FL_SAVE_REGS;
+
+	for (i = 0; i < argc; i++) {
+		ptr = argv[i];
+		last = 0;
+		for (token = next_token(&ptr, &last); token;
+		     token = next_token(&ptr, &last)) {
+			state = process_event(func_event, token, state);
+			if (state == FUNC_STATE_ERROR)
+				goto fail;
+		}
+	}
+	if (state != FUNC_STATE_END)
+		goto fail;
+
+	ret = ftrace_set_filter(&func_event->ops, func_event->func,
+				strlen(func_event->func), 0);
+	if (ret < 0)
+		goto fail;
+
+	ret = func_event_create(func_event);
+	if (ret < 0)
+		goto fail;
+
+	mutex_lock(&func_event_mutex);
+	list_add_tail(&func_event->list, &func_events);
+	mutex_unlock(&func_event_mutex);
+	return 0;
+ fail:
+	free_func_event(func_event);
+	return ret;
+}
+
+static void *func_event_seq_start(struct seq_file *m, loff_t *pos)
+{
+	mutex_lock(&func_event_mutex);
+	return seq_list_start(&func_events, *pos);
+}
+
+static void *func_event_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	return seq_list_next(v, &func_events, pos);
+}
+
+static void func_event_seq_stop(struct seq_file *m, void *v)
+{
+	mutex_unlock(&func_event_mutex);
+}
+
+static int func_event_seq_show(struct seq_file *m, void *v)
+{
+	struct func_event *func_event = v;
+
+	seq_printf(m, "%s()\n", func_event->func);
+
+	return 0;
+}
+
+static const struct seq_operations func_event_seq_op = {
+	.start  = func_event_seq_start,
+	.next   = func_event_seq_next,
+	.stop   = func_event_seq_stop,
+	.show   = func_event_seq_show
+};
+
+static int release_all_func_events(void)
+{
+	struct func_event *func_event, *n;
+	int ret = 0;
+
+	mutex_lock(&func_event_mutex);
+	list_for_each_entry_safe(func_event, n, &func_events, list) {
+		ret = trace_remove_event_call(&func_event->call);
+		if (ret < 0)
+			break;
+		list_del(&func_event->list);
+		free_func_event(func_event);
+	}
+	mutex_unlock(&func_event_mutex);
+	return ret;
+}
+
+static int func_event_open(struct inode *inode, struct file *file)
+{
+	int ret;
+
+	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
+		ret = release_all_func_events();
+		if (ret < 0)
+			return ret;
+	}
+
+	return seq_open(file, &func_event_seq_op);
+}
+
+static ssize_t
+func_event_write(struct file *filp, const char __user *ubuf,
+		 size_t cnt, loff_t *ppos)
+{
+	return trace_parse_run_command(filp, ubuf, cnt, ppos,
+				       create_function_event);
+}
+
+static const struct file_operations func_event_fops = {
+	.open		= func_event_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = seq_release,
+	.write		= func_event_write,
+};
+
+void create_function_event_file(struct dentry *d_tracer)
+{
+	struct dentry *d;
+
+	d = trace_create_file("function_events", 0644, d_tracer, NULL,
+			      &func_event_fops);
+	WARN(!d, "Failed to create function_events file");
+}
+
+/* Make a tracefs interface for controlling probe points */
+static __init int init_func_events(void)
+{
+	struct dentry *d_tracer;
+	struct dentry *entry;
+
+	d_tracer = tracing_init_dentry();
+	if (IS_ERR(d_tracer))
+		return 0;
+
+	entry = trace_create_file("function_events", 0644, d_tracer, NULL,
+				  &func_event_fops);
+
+	/* Event list interface */
+	if (!entry)
+		pr_warn("Could not create tracefs 'function-events' entry\n");
+
+	return 0;
+}
+fs_initcall(init_func_events);
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index fb66e3eaa192..a51caafd993b 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -49,17 +49,6 @@
 #define FIELD_STRING_RETIP	"__probe_ret_ip"
 #define FIELD_STRING_FUNC	"__probe_func"
 
-#undef DEFINE_FIELD
-#define DEFINE_FIELD(type, item, name, is_signed)			\
-	do {								\
-		ret = trace_define_field(event_call, #type, name,	\
-					 offsetof(typeof(field), item),	\
-					 sizeof(field.item), is_signed, \
-					 FILTER_OTHER);			\
-		if (ret)						\
-			return ret;					\
-	} while (0)
-
 
 /* Flags for trace_probe */
 #define TP_FLAG_TRACE		1
-- 
2.15.1