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Linux/kernel/events/callchain.c

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  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 "internal.h"
 15 
 16 struct callchain_cpus_entries {
 17         struct rcu_head                 rcu_head;
 18         struct perf_callchain_entry     *cpu_entries[0];
 19 };
 20 
 21 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
 22 static atomic_t nr_callchain_events;
 23 static DEFINE_MUTEX(callchain_mutex);
 24 static struct callchain_cpus_entries *callchain_cpus_entries;
 25 
 26 
 27 __weak void perf_callchain_kernel(struct perf_callchain_entry *entry,
 28                                   struct pt_regs *regs)
 29 {
 30 }
 31 
 32 __weak void perf_callchain_user(struct perf_callchain_entry *entry,
 33                                 struct pt_regs *regs)
 34 {
 35 }
 36 
 37 static void release_callchain_buffers_rcu(struct rcu_head *head)
 38 {
 39         struct callchain_cpus_entries *entries;
 40         int cpu;
 41 
 42         entries = container_of(head, struct callchain_cpus_entries, rcu_head);
 43 
 44         for_each_possible_cpu(cpu)
 45                 kfree(entries->cpu_entries[cpu]);
 46 
 47         kfree(entries);
 48 }
 49 
 50 static void release_callchain_buffers(void)
 51 {
 52         struct callchain_cpus_entries *entries;
 53 
 54         entries = callchain_cpus_entries;
 55         RCU_INIT_POINTER(callchain_cpus_entries, NULL);
 56         call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
 57 }
 58 
 59 static int alloc_callchain_buffers(void)
 60 {
 61         int cpu;
 62         int size;
 63         struct callchain_cpus_entries *entries;
 64 
 65         /*
 66          * We can't use the percpu allocation API for data that can be
 67          * accessed from NMI. Use a temporary manual per cpu allocation
 68          * until that gets sorted out.
 69          */
 70         size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
 71 
 72         entries = kzalloc(size, GFP_KERNEL);
 73         if (!entries)
 74                 return -ENOMEM;
 75 
 76         size = sizeof(struct perf_callchain_entry) * PERF_NR_CONTEXTS;
 77 
 78         for_each_possible_cpu(cpu) {
 79                 entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
 80                                                          cpu_to_node(cpu));
 81                 if (!entries->cpu_entries[cpu])
 82                         goto fail;
 83         }
 84 
 85         rcu_assign_pointer(callchain_cpus_entries, entries);
 86 
 87         return 0;
 88 
 89 fail:
 90         for_each_possible_cpu(cpu)
 91                 kfree(entries->cpu_entries[cpu]);
 92         kfree(entries);
 93 
 94         return -ENOMEM;
 95 }
 96 
 97 int get_callchain_buffers(void)
 98 {
 99         int err = 0;
100         int count;
101 
102         mutex_lock(&callchain_mutex);
103 
104         count = atomic_inc_return(&nr_callchain_events);
105         if (WARN_ON_ONCE(count < 1)) {
106                 err = -EINVAL;
107                 goto exit;
108         }
109 
110         if (count > 1) {
111                 /* If the allocation failed, give up */
112                 if (!callchain_cpus_entries)
113                         err = -ENOMEM;
114                 goto exit;
115         }
116 
117         err = alloc_callchain_buffers();
118 exit:
119         if (err)
120                 atomic_dec(&nr_callchain_events);
121 
122         mutex_unlock(&callchain_mutex);
123 
124         return err;
125 }
126 
127 void put_callchain_buffers(void)
128 {
129         if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
130                 release_callchain_buffers();
131                 mutex_unlock(&callchain_mutex);
132         }
133 }
134 
135 static struct perf_callchain_entry *get_callchain_entry(int *rctx)
136 {
137         int cpu;
138         struct callchain_cpus_entries *entries;
139 
140         *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
141         if (*rctx == -1)
142                 return NULL;
143 
144         entries = rcu_dereference(callchain_cpus_entries);
145         if (!entries)
146                 return NULL;
147 
148         cpu = smp_processor_id();
149 
150         return &entries->cpu_entries[cpu][*rctx];
151 }
152 
153 static void
154 put_callchain_entry(int rctx)
155 {
156         put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
157 }
158 
159 struct perf_callchain_entry *
160 perf_callchain(struct perf_event *event, struct pt_regs *regs)
161 {
162         int rctx;
163         struct perf_callchain_entry *entry;
164 
165         int kernel = !event->attr.exclude_callchain_kernel;
166         int user   = !event->attr.exclude_callchain_user;
167 
168         if (!kernel && !user)
169                 return NULL;
170 
171         entry = get_callchain_entry(&rctx);
172         if (rctx == -1)
173                 return NULL;
174 
175         if (!entry)
176                 goto exit_put;
177 
178         entry->nr = 0;
179 
180         if (kernel && !user_mode(regs)) {
181                 perf_callchain_store(entry, PERF_CONTEXT_KERNEL);
182                 perf_callchain_kernel(entry, regs);
183         }
184 
185         if (user) {
186                 if (!user_mode(regs)) {
187                         if  (current->mm)
188                                 regs = task_pt_regs(current);
189                         else
190                                 regs = NULL;
191                 }
192 
193                 if (regs) {
194                         /*
195                          * Disallow cross-task user callchains.
196                          */
197                         if (event->ctx->task && event->ctx->task != current)
198                                 goto exit_put;
199 
200                         perf_callchain_store(entry, PERF_CONTEXT_USER);
201                         perf_callchain_user(entry, regs);
202                 }
203         }
204 
205 exit_put:
206         put_callchain_entry(rctx);
207 
208         return entry;
209 }
210 

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