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Linux/kernel/events/callchain.c

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  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 
 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 
 38 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
 39                                   struct pt_regs *regs)
 40 {
 41 }
 42 
 43 __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
 44                                 struct pt_regs *regs)
 45 {
 46 }
 47 
 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 
 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 
 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 
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 
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 
152 static 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                 return NULL;
164 
165         cpu = smp_processor_id();
166 
167         return (((void *)entries->cpu_entries[cpu]) +
168                 (*rctx * perf_callchain_entry__sizeof()));
169 }
170 
171 static void
172 put_callchain_entry(int rctx)
173 {
174         put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
175 }
176 
177 struct perf_callchain_entry *
178 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
179                    u32 max_stack, bool crosstask, bool add_mark)
180 {
181         struct perf_callchain_entry *entry;
182         struct perf_callchain_entry_ctx ctx;
183         int rctx;
184 
185         entry = get_callchain_entry(&rctx);
186         if (rctx == -1)
187                 return NULL;
188 
189         if (!entry)
190                 goto exit_put;
191 
192         ctx.entry     = entry;
193         ctx.max_stack = max_stack;
194         ctx.nr        = entry->nr = init_nr;
195         ctx.contexts       = 0;
196         ctx.contexts_maxed = false;
197 
198         if (kernel && !user_mode(regs)) {
199                 if (add_mark)
200                         perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
201                 perf_callchain_kernel(&ctx, regs);
202         }
203 
204         if (user) {
205                 if (!user_mode(regs)) {
206                         if  (current->mm)
207                                 regs = task_pt_regs(current);
208                         else
209                                 regs = NULL;
210                 }
211 
212                 if (regs) {
213                         mm_segment_t fs;
214 
215                         if (crosstask)
216                                 goto exit_put;
217 
218                         if (add_mark)
219                                 perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
220 
221                         fs = get_fs();
222                         set_fs(USER_DS);
223                         perf_callchain_user(&ctx, regs);
224                         set_fs(fs);
225                 }
226         }
227 
228 exit_put:
229         put_callchain_entry(rctx);
230 
231         return entry;
232 }
233 
234 /*
235  * Used for sysctl_perf_event_max_stack and
236  * sysctl_perf_event_max_contexts_per_stack.
237  */
238 int perf_event_max_stack_handler(struct ctl_table *table, int write,
239                                  void *buffer, size_t *lenp, loff_t *ppos)
240 {
241         int *value = table->data;
242         int new_value = *value, ret;
243         struct ctl_table new_table = *table;
244 
245         new_table.data = &new_value;
246         ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
247         if (ret || !write)
248                 return ret;
249 
250         mutex_lock(&callchain_mutex);
251         if (atomic_read(&nr_callchain_events))
252                 ret = -EBUSY;
253         else
254                 *value = new_value;
255 
256         mutex_unlock(&callchain_mutex);
257 
258         return ret;
259 }
260 

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