1 /*
2 * Performance events callchain code, extracted from core.c:
3 *
4 * Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
5 * Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
6 * Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
7 * Copyright � 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
8 *
9 * For licensing details see kernel-base/COPYING
10 */
11
12 #include <linux/perf_event.h>
13 #include <linux/slab.h>
14 #include <linux/sched/task_stack.h>
15
16 #include "internal.h"
17
18 struct callchain_cpus_entries {
19 struct rcu_head rcu_head;
20 struct perf_callchain_entry *cpu_entries[0];
21 };
22
23 int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
24 int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;
25
perf_callchain_entry__sizeof(void)26 static inline size_t perf_callchain_entry__sizeof(void)
27 {
28 return (sizeof(struct perf_callchain_entry) +
29 sizeof(__u64) * (sysctl_perf_event_max_stack +
30 sysctl_perf_event_max_contexts_per_stack));
31 }
32
33 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
34 static atomic_t nr_callchain_events;
35 static DEFINE_MUTEX(callchain_mutex);
36 static struct callchain_cpus_entries *callchain_cpus_entries;
37
38
perf_callchain_kernel(struct perf_callchain_entry_ctx * entry,struct pt_regs * regs)39 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
40 struct pt_regs *regs)
41 {
42 }
43
perf_callchain_user(struct perf_callchain_entry_ctx * entry,struct pt_regs * regs)44 __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
45 struct pt_regs *regs)
46 {
47 }
48
release_callchain_buffers_rcu(struct rcu_head * head)49 static void release_callchain_buffers_rcu(struct rcu_head *head)
50 {
51 struct callchain_cpus_entries *entries;
52 int cpu;
53
54 entries = container_of(head, struct callchain_cpus_entries, rcu_head);
55
56 for_each_possible_cpu(cpu)
57 kfree(entries->cpu_entries[cpu]);
58
59 kfree(entries);
60 }
61
release_callchain_buffers(void)62 static void release_callchain_buffers(void)
63 {
64 struct callchain_cpus_entries *entries;
65
66 entries = callchain_cpus_entries;
67 RCU_INIT_POINTER(callchain_cpus_entries, NULL);
68 call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
69 }
70
alloc_callchain_buffers(void)71 static int alloc_callchain_buffers(void)
72 {
73 int cpu;
74 int size;
75 struct callchain_cpus_entries *entries;
76
77 /*
78 * We can't use the percpu allocation API for data that can be
79 * accessed from NMI. Use a temporary manual per cpu allocation
80 * until that gets sorted out.
81 */
82 size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
83
84 entries = kzalloc(size, GFP_KERNEL);
85 if (!entries)
86 return -ENOMEM;
87
88 size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
89
90 for_each_possible_cpu(cpu) {
91 entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
92 cpu_to_node(cpu));
93 if (!entries->cpu_entries[cpu])
94 goto fail;
95 }
96
97 rcu_assign_pointer(callchain_cpus_entries, entries);
98
99 return 0;
100
101 fail:
102 for_each_possible_cpu(cpu)
103 kfree(entries->cpu_entries[cpu]);
104 kfree(entries);
105
106 return -ENOMEM;
107 }
108
get_callchain_buffers(int event_max_stack)109 int get_callchain_buffers(int event_max_stack)
110 {
111 int err = 0;
112 int count;
113
114 mutex_lock(&callchain_mutex);
115
116 count = atomic_inc_return(&nr_callchain_events);
117 if (WARN_ON_ONCE(count < 1)) {
118 err = -EINVAL;
119 goto exit;
120 }
121
122 /*
123 * If requesting per event more than the global cap,
124 * return a different error to help userspace figure
125 * this out.
126 *
127 * And also do it here so that we have &callchain_mutex held.
128 */
129 if (event_max_stack > sysctl_perf_event_max_stack) {
130 err = -EOVERFLOW;
131 goto exit;
132 }
133
134 if (count == 1)
135 err = alloc_callchain_buffers();
136 exit:
137 if (err)
138 atomic_dec(&nr_callchain_events);
139
140 mutex_unlock(&callchain_mutex);
141
142 return err;
143 }
144
put_callchain_buffers(void)145 void put_callchain_buffers(void)
146 {
147 if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
148 release_callchain_buffers();
149 mutex_unlock(&callchain_mutex);
150 }
151 }
152
get_callchain_entry(int * rctx)153 static struct perf_callchain_entry *get_callchain_entry(int *rctx)
154 {
155 int cpu;
156 struct callchain_cpus_entries *entries;
157
158 *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
159 if (*rctx == -1)
160 return NULL;
161
162 entries = rcu_dereference(callchain_cpus_entries);
163 if (!entries)
164 return NULL;
165
166 cpu = smp_processor_id();
167
168 return (((void *)entries->cpu_entries[cpu]) +
169 (*rctx * perf_callchain_entry__sizeof()));
170 }
171
172 static void
put_callchain_entry(int rctx)173 put_callchain_entry(int rctx)
174 {
175 put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
176 }
177
178 struct perf_callchain_entry *
perf_callchain(struct perf_event * event,struct pt_regs * regs)179 perf_callchain(struct perf_event *event, struct pt_regs *regs)
180 {
181 bool kernel = !event->attr.exclude_callchain_kernel;
182 bool user = !event->attr.exclude_callchain_user;
183 /* Disallow cross-task user callchains. */
184 bool crosstask = event->ctx->task && event->ctx->task != current;
185 const u32 max_stack = event->attr.sample_max_stack;
186
187 if (!kernel && !user)
188 return NULL;
189
190 return get_perf_callchain(regs, 0, kernel, user, max_stack, crosstask, true);
191 }
192
193 struct perf_callchain_entry *
get_perf_callchain(struct pt_regs * regs,u32 init_nr,bool kernel,bool user,u32 max_stack,bool crosstask,bool add_mark)194 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
195 u32 max_stack, bool crosstask, bool add_mark)
196 {
197 struct perf_callchain_entry *entry;
198 struct perf_callchain_entry_ctx ctx;
199 int rctx;
200
201 entry = get_callchain_entry(&rctx);
202 if (rctx == -1)
203 return NULL;
204
205 if (!entry)
206 goto exit_put;
207
208 ctx.entry = entry;
209 ctx.max_stack = max_stack;
210 ctx.nr = entry->nr = init_nr;
211 ctx.contexts = 0;
212 ctx.contexts_maxed = false;
213
214 if (kernel && !user_mode(regs)) {
215 if (add_mark)
216 perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
217 perf_callchain_kernel(&ctx, regs);
218 }
219
220 if (user) {
221 if (!user_mode(regs)) {
222 if (current->mm)
223 regs = task_pt_regs(current);
224 else
225 regs = NULL;
226 }
227
228 if (regs) {
229 mm_segment_t fs;
230
231 if (crosstask)
232 goto exit_put;
233
234 if (add_mark)
235 perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
236
237 fs = get_fs();
238 set_fs(USER_DS);
239 perf_callchain_user(&ctx, regs);
240 set_fs(fs);
241 }
242 }
243
244 exit_put:
245 put_callchain_entry(rctx);
246
247 return entry;
248 }
249
250 /*
251 * Used for sysctl_perf_event_max_stack and
252 * sysctl_perf_event_max_contexts_per_stack.
253 */
perf_event_max_stack_handler(struct ctl_table * table,int write,void __user * buffer,size_t * lenp,loff_t * ppos)254 int perf_event_max_stack_handler(struct ctl_table *table, int write,
255 void __user *buffer, size_t *lenp, loff_t *ppos)
256 {
257 int *value = table->data;
258 int new_value = *value, ret;
259 struct ctl_table new_table = *table;
260
261 new_table.data = &new_value;
262 ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
263 if (ret || !write)
264 return ret;
265
266 mutex_lock(&callchain_mutex);
267 if (atomic_read(&nr_callchain_events))
268 ret = -EBUSY;
269 else
270 *value = new_value;
271
272 mutex_unlock(&callchain_mutex);
273
274 return ret;
275 }
276