xref: /openbmc/linux/kernel/events/callchain.c (revision 967747bb)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Performance events callchain code, extracted from core.c:
4  *
5  *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
6  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
7  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
8  *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
9  */
10 
11 #include <linux/perf_event.h>
12 #include <linux/slab.h>
13 #include <linux/sched/task_stack.h>
14 
15 #include "internal.h"
16 
17 struct callchain_cpus_entries {
18 	struct rcu_head			rcu_head;
19 	struct perf_callchain_entry	*cpu_entries[];
20 };
21 
22 int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
23 int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;
24 
perf_callchain_entry__sizeof(void)25 static inline size_t perf_callchain_entry__sizeof(void)
26 {
27 	return (sizeof(struct perf_callchain_entry) +
28 		sizeof(__u64) * (sysctl_perf_event_max_stack +
29 				 sysctl_perf_event_max_contexts_per_stack));
30 }
31 
32 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
33 static atomic_t nr_callchain_events;
34 static DEFINE_MUTEX(callchain_mutex);
35 static struct callchain_cpus_entries *callchain_cpus_entries;
36 
37 
perf_callchain_kernel(struct perf_callchain_entry_ctx * entry,struct pt_regs * regs)38 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
39 				  struct pt_regs *regs)
40 {
41 }
42 
perf_callchain_user(struct perf_callchain_entry_ctx * entry,struct pt_regs * regs)43 __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
44 				struct pt_regs *regs)
45 {
46 }
47 
release_callchain_buffers_rcu(struct rcu_head * head)48 static void release_callchain_buffers_rcu(struct rcu_head *head)
49 {
50 	struct callchain_cpus_entries *entries;
51 	int cpu;
52 
53 	entries = container_of(head, struct callchain_cpus_entries, rcu_head);
54 
55 	for_each_possible_cpu(cpu)
56 		kfree(entries->cpu_entries[cpu]);
57 
58 	kfree(entries);
59 }
60 
release_callchain_buffers(void)61 static void release_callchain_buffers(void)
62 {
63 	struct callchain_cpus_entries *entries;
64 
65 	entries = callchain_cpus_entries;
66 	RCU_INIT_POINTER(callchain_cpus_entries, NULL);
67 	call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
68 }
69 
alloc_callchain_buffers(void)70 static int alloc_callchain_buffers(void)
71 {
72 	int cpu;
73 	int size;
74 	struct callchain_cpus_entries *entries;
75 
76 	/*
77 	 * We can't use the percpu allocation API for data that can be
78 	 * accessed from NMI. Use a temporary manual per cpu allocation
79 	 * until that gets sorted out.
80 	 */
81 	size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
82 
83 	entries = kzalloc(size, GFP_KERNEL);
84 	if (!entries)
85 		return -ENOMEM;
86 
87 	size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
88 
89 	for_each_possible_cpu(cpu) {
90 		entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
91 							 cpu_to_node(cpu));
92 		if (!entries->cpu_entries[cpu])
93 			goto fail;
94 	}
95 
96 	rcu_assign_pointer(callchain_cpus_entries, entries);
97 
98 	return 0;
99 
100 fail:
101 	for_each_possible_cpu(cpu)
102 		kfree(entries->cpu_entries[cpu]);
103 	kfree(entries);
104 
105 	return -ENOMEM;
106 }
107 
get_callchain_buffers(int event_max_stack)108 int get_callchain_buffers(int event_max_stack)
109 {
110 	int err = 0;
111 	int count;
112 
113 	mutex_lock(&callchain_mutex);
114 
115 	count = atomic_inc_return(&nr_callchain_events);
116 	if (WARN_ON_ONCE(count < 1)) {
117 		err = -EINVAL;
118 		goto exit;
119 	}
120 
121 	/*
122 	 * If requesting per event more than the global cap,
123 	 * return a different error to help userspace figure
124 	 * this out.
125 	 *
126 	 * And also do it here so that we have &callchain_mutex held.
127 	 */
128 	if (event_max_stack > sysctl_perf_event_max_stack) {
129 		err = -EOVERFLOW;
130 		goto exit;
131 	}
132 
133 	if (count == 1)
134 		err = alloc_callchain_buffers();
135 exit:
136 	if (err)
137 		atomic_dec(&nr_callchain_events);
138 
139 	mutex_unlock(&callchain_mutex);
140 
141 	return err;
142 }
143 
put_callchain_buffers(void)144 void put_callchain_buffers(void)
145 {
146 	if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
147 		release_callchain_buffers();
148 		mutex_unlock(&callchain_mutex);
149 	}
150 }
151 
get_callchain_entry(int * rctx)152 struct perf_callchain_entry *get_callchain_entry(int *rctx)
153 {
154 	int cpu;
155 	struct callchain_cpus_entries *entries;
156 
157 	*rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
158 	if (*rctx == -1)
159 		return NULL;
160 
161 	entries = rcu_dereference(callchain_cpus_entries);
162 	if (!entries) {
163 		put_recursion_context(this_cpu_ptr(callchain_recursion), *rctx);
164 		return NULL;
165 	}
166 
167 	cpu = smp_processor_id();
168 
169 	return (((void *)entries->cpu_entries[cpu]) +
170 		(*rctx * perf_callchain_entry__sizeof()));
171 }
172 
173 void
put_callchain_entry(int rctx)174 put_callchain_entry(int rctx)
175 {
176 	put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
177 }
178 
179 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)180 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
181 		   u32 max_stack, bool crosstask, bool add_mark)
182 {
183 	struct perf_callchain_entry *entry;
184 	struct perf_callchain_entry_ctx ctx;
185 	int rctx;
186 
187 	entry = get_callchain_entry(&rctx);
188 	if (!entry)
189 		return NULL;
190 
191 	ctx.entry     = entry;
192 	ctx.max_stack = max_stack;
193 	ctx.nr	      = entry->nr = init_nr;
194 	ctx.contexts       = 0;
195 	ctx.contexts_maxed = false;
196 
197 	if (kernel && !user_mode(regs)) {
198 		if (add_mark)
199 			perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
200 		perf_callchain_kernel(&ctx, regs);
201 	}
202 
203 	if (user) {
204 		if (!user_mode(regs)) {
205 			if  (current->mm)
206 				regs = task_pt_regs(current);
207 			else
208 				regs = NULL;
209 		}
210 
211 		if (regs) {
212 			if (crosstask)
213 				goto exit_put;
214 
215 			if (add_mark)
216 				perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
217 
218 			perf_callchain_user(&ctx, regs);
219 		}
220 	}
221 
222 exit_put:
223 	put_callchain_entry(rctx);
224 
225 	return entry;
226 }
227 
228 /*
229  * Used for sysctl_perf_event_max_stack and
230  * sysctl_perf_event_max_contexts_per_stack.
231  */
perf_event_max_stack_handler(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)232 int perf_event_max_stack_handler(struct ctl_table *table, int write,
233 				 void *buffer, size_t *lenp, loff_t *ppos)
234 {
235 	int *value = table->data;
236 	int new_value = *value, ret;
237 	struct ctl_table new_table = *table;
238 
239 	new_table.data = &new_value;
240 	ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
241 	if (ret || !write)
242 		return ret;
243 
244 	mutex_lock(&callchain_mutex);
245 	if (atomic_read(&nr_callchain_events))
246 		ret = -EBUSY;
247 	else
248 		*value = new_value;
249 
250 	mutex_unlock(&callchain_mutex);
251 
252 	return ret;
253 }
254