1 /*
2  * trace event based perf event profiling/tracing
3  *
4  * Copyright (C) 2009 Red Hat Inc, Peter Zijlstra <pzijlstr@redhat.com>
5  * Copyright (C) 2009-2010 Frederic Weisbecker <fweisbec@gmail.com>
6  */
7 
8 #include <linux/module.h>
9 #include <linux/kprobes.h>
10 #include "trace.h"
11 
12 DEFINE_PER_CPU(struct pt_regs, perf_trace_regs);
13 
14 static char *perf_trace_buf;
15 static char *perf_trace_buf_nmi;
16 
17 typedef typeof(char [PERF_MAX_TRACE_SIZE]) perf_trace_t ;
18 
19 /* Count the events in use (per event id, not per instance) */
20 static int	total_ref_count;
21 
22 static int perf_trace_event_enable(struct ftrace_event_call *event)
23 {
24 	char *buf;
25 	int ret = -ENOMEM;
26 
27 	if (event->perf_refcount++ > 0)
28 		return 0;
29 
30 	if (!total_ref_count) {
31 		buf = (char *)alloc_percpu(perf_trace_t);
32 		if (!buf)
33 			goto fail_buf;
34 
35 		rcu_assign_pointer(perf_trace_buf, buf);
36 
37 		buf = (char *)alloc_percpu(perf_trace_t);
38 		if (!buf)
39 			goto fail_buf_nmi;
40 
41 		rcu_assign_pointer(perf_trace_buf_nmi, buf);
42 	}
43 
44 	ret = event->perf_event_enable(event);
45 	if (!ret) {
46 		total_ref_count++;
47 		return 0;
48 	}
49 
50 fail_buf_nmi:
51 	if (!total_ref_count) {
52 		free_percpu(perf_trace_buf_nmi);
53 		free_percpu(perf_trace_buf);
54 		perf_trace_buf_nmi = NULL;
55 		perf_trace_buf = NULL;
56 	}
57 fail_buf:
58 	event->perf_refcount--;
59 
60 	return ret;
61 }
62 
63 int perf_trace_enable(int event_id)
64 {
65 	struct ftrace_event_call *event;
66 	int ret = -EINVAL;
67 
68 	mutex_lock(&event_mutex);
69 	list_for_each_entry(event, &ftrace_events, list) {
70 		if (event->id == event_id && event->perf_event_enable &&
71 		    try_module_get(event->mod)) {
72 			ret = perf_trace_event_enable(event);
73 			break;
74 		}
75 	}
76 	mutex_unlock(&event_mutex);
77 
78 	return ret;
79 }
80 
81 static void perf_trace_event_disable(struct ftrace_event_call *event)
82 {
83 	char *buf, *nmi_buf;
84 
85 	if (--event->perf_refcount > 0)
86 		return;
87 
88 	event->perf_event_disable(event);
89 
90 	if (!--total_ref_count) {
91 		buf = perf_trace_buf;
92 		rcu_assign_pointer(perf_trace_buf, NULL);
93 
94 		nmi_buf = perf_trace_buf_nmi;
95 		rcu_assign_pointer(perf_trace_buf_nmi, NULL);
96 
97 		/*
98 		 * Ensure every events in profiling have finished before
99 		 * releasing the buffers
100 		 */
101 		synchronize_sched();
102 
103 		free_percpu(buf);
104 		free_percpu(nmi_buf);
105 	}
106 }
107 
108 void perf_trace_disable(int event_id)
109 {
110 	struct ftrace_event_call *event;
111 
112 	mutex_lock(&event_mutex);
113 	list_for_each_entry(event, &ftrace_events, list) {
114 		if (event->id == event_id) {
115 			perf_trace_event_disable(event);
116 			module_put(event->mod);
117 			break;
118 		}
119 	}
120 	mutex_unlock(&event_mutex);
121 }
122 
123 __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
124 				       int *rctxp, unsigned long *irq_flags)
125 {
126 	struct trace_entry *entry;
127 	char *trace_buf, *raw_data;
128 	int pc, cpu;
129 
130 	pc = preempt_count();
131 
132 	/* Protect the per cpu buffer, begin the rcu read side */
133 	local_irq_save(*irq_flags);
134 
135 	*rctxp = perf_swevent_get_recursion_context();
136 	if (*rctxp < 0)
137 		goto err_recursion;
138 
139 	cpu = smp_processor_id();
140 
141 	if (in_nmi())
142 		trace_buf = rcu_dereference(perf_trace_buf_nmi);
143 	else
144 		trace_buf = rcu_dereference(perf_trace_buf);
145 
146 	if (!trace_buf)
147 		goto err;
148 
149 	raw_data = per_cpu_ptr(trace_buf, cpu);
150 
151 	/* zero the dead bytes from align to not leak stack to user */
152 	*(u64 *)(&raw_data[size - sizeof(u64)]) = 0ULL;
153 
154 	entry = (struct trace_entry *)raw_data;
155 	tracing_generic_entry_update(entry, *irq_flags, pc);
156 	entry->type = type;
157 
158 	return raw_data;
159 err:
160 	perf_swevent_put_recursion_context(*rctxp);
161 err_recursion:
162 	local_irq_restore(*irq_flags);
163 	return NULL;
164 }
165 EXPORT_SYMBOL_GPL(perf_trace_buf_prepare);
166