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 EXPORT_PER_CPU_SYMBOL_GPL(perf_trace_regs);
14 
15 EXPORT_SYMBOL_GPL(perf_arch_fetch_caller_regs);
16 
17 static char *perf_trace_buf;
18 static char *perf_trace_buf_nmi;
19 
20 /*
21  * Force it to be aligned to unsigned long to avoid misaligned accesses
22  * suprises
23  */
24 typedef typeof(unsigned long [PERF_MAX_TRACE_SIZE / sizeof(unsigned long)])
25 	perf_trace_t;
26 
27 /* Count the events in use (per event id, not per instance) */
28 static int	total_ref_count;
29 
30 static int perf_trace_event_enable(struct ftrace_event_call *event)
31 {
32 	char *buf;
33 	int ret = -ENOMEM;
34 
35 	if (event->perf_refcount++ > 0)
36 		return 0;
37 
38 	if (!total_ref_count) {
39 		buf = (char *)alloc_percpu(perf_trace_t);
40 		if (!buf)
41 			goto fail_buf;
42 
43 		rcu_assign_pointer(perf_trace_buf, buf);
44 
45 		buf = (char *)alloc_percpu(perf_trace_t);
46 		if (!buf)
47 			goto fail_buf_nmi;
48 
49 		rcu_assign_pointer(perf_trace_buf_nmi, buf);
50 	}
51 
52 	ret = event->perf_event_enable(event);
53 	if (!ret) {
54 		total_ref_count++;
55 		return 0;
56 	}
57 
58 fail_buf_nmi:
59 	if (!total_ref_count) {
60 		free_percpu(perf_trace_buf_nmi);
61 		free_percpu(perf_trace_buf);
62 		perf_trace_buf_nmi = NULL;
63 		perf_trace_buf = NULL;
64 	}
65 fail_buf:
66 	event->perf_refcount--;
67 
68 	return ret;
69 }
70 
71 int perf_trace_enable(int event_id)
72 {
73 	struct ftrace_event_call *event;
74 	int ret = -EINVAL;
75 
76 	mutex_lock(&event_mutex);
77 	list_for_each_entry(event, &ftrace_events, list) {
78 		if (event->id == event_id && event->perf_event_enable &&
79 		    try_module_get(event->mod)) {
80 			ret = perf_trace_event_enable(event);
81 			break;
82 		}
83 	}
84 	mutex_unlock(&event_mutex);
85 
86 	return ret;
87 }
88 
89 static void perf_trace_event_disable(struct ftrace_event_call *event)
90 {
91 	char *buf, *nmi_buf;
92 
93 	if (--event->perf_refcount > 0)
94 		return;
95 
96 	event->perf_event_disable(event);
97 
98 	if (!--total_ref_count) {
99 		buf = perf_trace_buf;
100 		rcu_assign_pointer(perf_trace_buf, NULL);
101 
102 		nmi_buf = perf_trace_buf_nmi;
103 		rcu_assign_pointer(perf_trace_buf_nmi, NULL);
104 
105 		/*
106 		 * Ensure every events in profiling have finished before
107 		 * releasing the buffers
108 		 */
109 		synchronize_sched();
110 
111 		free_percpu(buf);
112 		free_percpu(nmi_buf);
113 	}
114 }
115 
116 void perf_trace_disable(int event_id)
117 {
118 	struct ftrace_event_call *event;
119 
120 	mutex_lock(&event_mutex);
121 	list_for_each_entry(event, &ftrace_events, list) {
122 		if (event->id == event_id) {
123 			perf_trace_event_disable(event);
124 			module_put(event->mod);
125 			break;
126 		}
127 	}
128 	mutex_unlock(&event_mutex);
129 }
130 
131 __kprobes void *perf_trace_buf_prepare(int size, unsigned short type,
132 				       int *rctxp, unsigned long *irq_flags)
133 {
134 	struct trace_entry *entry;
135 	char *trace_buf, *raw_data;
136 	int pc, cpu;
137 
138 	BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(unsigned long));
139 
140 	pc = preempt_count();
141 
142 	/* Protect the per cpu buffer, begin the rcu read side */
143 	local_irq_save(*irq_flags);
144 
145 	*rctxp = perf_swevent_get_recursion_context();
146 	if (*rctxp < 0)
147 		goto err_recursion;
148 
149 	cpu = smp_processor_id();
150 
151 	if (in_nmi())
152 		trace_buf = rcu_dereference_sched(perf_trace_buf_nmi);
153 	else
154 		trace_buf = rcu_dereference_sched(perf_trace_buf);
155 
156 	if (!trace_buf)
157 		goto err;
158 
159 	raw_data = per_cpu_ptr(trace_buf, cpu);
160 
161 	/* zero the dead bytes from align to not leak stack to user */
162 	memset(&raw_data[size - sizeof(u64)], 0, sizeof(u64));
163 
164 	entry = (struct trace_entry *)raw_data;
165 	tracing_generic_entry_update(entry, *irq_flags, pc);
166 	entry->type = type;
167 
168 	return raw_data;
169 err:
170 	perf_swevent_put_recursion_context(*rctxp);
171 err_recursion:
172 	local_irq_restore(*irq_flags);
173 	return NULL;
174 }
175 EXPORT_SYMBOL_GPL(perf_trace_buf_prepare);
176