kernel/events/callchain.c

   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 int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
  22
  23 static inline size_t perf_callchain_entry__sizeof(void)
  24 {
  25         return (sizeof(struct perf_callchain_entry) +
  26                 sizeof(__u64) * sysctl_perf_event_max_stack);
  27 }
  28
  29 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
  30 static atomic_t nr_callchain_events;
  31 static DEFINE_MUTEX(callchain_mutex);
  32 static struct callchain_cpus_entries *callchain_cpus_entries;
  33
  34
  35 __weak void perf_callchain_kernel(struct perf_callchain_entry *entry,
  36                                   struct pt_regs *regs)
  37 {
  38 }
  39
  40 __weak void perf_callchain_user(struct perf_callchain_entry *entry,
  41                                 struct pt_regs *regs)
  42 {
  43 }
  44
  45 static void release_callchain_buffers_rcu(struct rcu_head *head)
  46 {
  47         struct callchain_cpus_entries *entries;
  48         int cpu;
  49
  50         entries = container_of(head, struct callchain_cpus_entries, rcu_head);
  51
  52         for_each_possible_cpu(cpu)
  53                 kfree(entries->cpu_entries[cpu]);
  54
  55         kfree(entries);
  56 }
  57
  58 static void release_callchain_buffers(void)
  59 {
  60         struct callchain_cpus_entries *entries;
  61
  62         entries = callchain_cpus_entries;
  63         RCU_INIT_POINTER(callchain_cpus_entries, NULL);
  64         call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
  65 }
  66
  67 static int alloc_callchain_buffers(void)
  68 {
  69         int cpu;
  70         int size;
  71         struct callchain_cpus_entries *entries;
  72
  73         /*
  74          * We can't use the percpu allocation API for data that can be
  75          * accessed from NMI. Use a temporary manual per cpu allocation
  76          * until that gets sorted out.
  77          */
  78         size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
  79
  80         entries = kzalloc(size, GFP_KERNEL);
  81         if (!entries)
  82                 return -ENOMEM;
  83
  84         size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
  85
  86         for_each_possible_cpu(cpu) {
  87                 entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
  88                                                          cpu_to_node(cpu));
  89                 if (!entries->cpu_entries[cpu])
  90                         goto fail;
  91         }
  92
  93         rcu_assign_pointer(callchain_cpus_entries, entries);
  94
  95         return 0;
  96
  97 fail:
  98         for_each_possible_cpu(cpu)
  99                 kfree(entries->cpu_entries[cpu]);
 100         kfree(entries);
 101
 102         return -ENOMEM;
 103 }
 104
 105 int get_callchain_buffers(void)
 106 {
 107         int err = 0;
 108         int count;
 109
 110         mutex_lock(&callchain_mutex);
 111
 112         count = atomic_inc_return(&nr_callchain_events);
 113         if (WARN_ON_ONCE(count < 1)) {
 114                 err = -EINVAL;
 115                 goto exit;
 116         }
 117
 118         if (count > 1) {
 119                 /* If the allocation failed, give up */
 120                 if (!callchain_cpus_entries)
 121                         err = -ENOMEM;
 122                 goto exit;
 123         }
 124
 125         err = alloc_callchain_buffers();
 126 exit:
 127         if (err)
 128                 atomic_dec(&nr_callchain_events);
 129
 130         mutex_unlock(&callchain_mutex);
 131
 132         return err;
 133 }
 134
 135 void put_callchain_buffers(void)
 136 {
 137         if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
 138                 release_callchain_buffers();
 139                 mutex_unlock(&callchain_mutex);
 140         }
 141 }
 142
 143 static struct perf_callchain_entry *get_callchain_entry(int *rctx)
 144 {
 145         int cpu;
 146         struct callchain_cpus_entries *entries;
 147
 148         *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
 149         if (*rctx == -1)
 150                 return NULL;
 151
 152         entries = rcu_dereference(callchain_cpus_entries);
 153         if (!entries)
 154                 return NULL;
 155
 156         cpu = smp_processor_id();
 157
 158         return (((void *)entries->cpu_entries[cpu]) +
 159                 (*rctx * perf_callchain_entry__sizeof()));
 160 }
 161
 162 static void
 163 put_callchain_entry(int rctx)
 164 {
 165         put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
 166 }
 167
 168 struct perf_callchain_entry *
 169 perf_callchain(struct perf_event *event, struct pt_regs *regs)
 170 {
 171         bool kernel = !event->attr.exclude_callchain_kernel;
 172         bool user   = !event->attr.exclude_callchain_user;
 173         /* Disallow cross-task user callchains. */
 174         bool crosstask = event->ctx->task && event->ctx->task != current;
 175
 176         if (!kernel && !user)
 177                 return NULL;
 178
 179         return get_perf_callchain(regs, 0, kernel, user, crosstask, true);
 180 }
 181
 182 struct perf_callchain_entry *
 183 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
 184                    bool crosstask, bool add_mark)
 185 {
 186         struct perf_callchain_entry *entry;
 187         int rctx;
 188
 189         entry = get_callchain_entry(&rctx);
 190         if (rctx == -1)
 191                 return NULL;
 192
 193         if (!entry)
 194                 goto exit_put;
 195
 196         entry->nr = init_nr;
 197
 198         if (kernel && !user_mode(regs)) {
 199                 if (add_mark)
 200                         perf_callchain_store(entry, PERF_CONTEXT_KERNEL);
 201                 perf_callchain_kernel(entry, 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                         if (crosstask)
 214                                 goto exit_put;
 215
 216                         if (add_mark)
 217                                 perf_callchain_store(entry, PERF_CONTEXT_USER);
 218                         perf_callchain_user(entry, regs);
 219                 }
 220         }
 221
 222 exit_put:
 223         put_callchain_entry(rctx);
 224
 225         return entry;
 226 }
 227
 228 int perf_event_max_stack_handler(struct ctl_table *table, int write,
 229                                  void __user *buffer, size_t *lenp, loff_t *ppos)
 230 {
 231         int new_value = sysctl_perf_event_max_stack, ret;
 232         struct ctl_table new_table = *table;
 233
 234         new_table.data = &new_value;
 235         ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
 236         if (ret || !write)
 237                 return ret;
 238
 239         mutex_lock(&callchain_mutex);
 240         if (atomic_read(&nr_callchain_events))
 241                 ret = -EBUSY;
 242         else
 243                 sysctl_perf_event_max_stack = new_value;
 244
 245         mutex_unlock(&callchain_mutex);
 246
 247         return ret;
 248 }