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 <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
  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
  39 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
  40                                   struct pt_regs *regs)
  41 {
  42 }
  43
  44 __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
  45                                 struct pt_regs *regs)
  46 {
  47 }
  48
  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
  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
  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
 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         if (count > 1) {
 123                 /* If the allocation failed, give up */
 124                 if (!callchain_cpus_entries)
 125                         err = -ENOMEM;
 126                 /*
 127                  * If requesting per event more than the global cap,
 128                  * return a different error to help userspace figure
 129                  * this out.
 130                  *
 131                  * And also do it here so that we have &callchain_mutex held.
 132                  */
 133                 if (event_max_stack > sysctl_perf_event_max_stack)
 134                         err = -EOVERFLOW;
 135                 goto exit;
 136         }
 137
 138         err = alloc_callchain_buffers();
 139 exit:
 140         if (err)
 141                 atomic_dec(&nr_callchain_events);
 142
 143         mutex_unlock(&callchain_mutex);
 144
 145         return err;
 146 }
 147
 148 void put_callchain_buffers(void)
 149 {
 150         if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
 151                 release_callchain_buffers();
 152                 mutex_unlock(&callchain_mutex);
 153         }
 154 }
 155
 156 static struct perf_callchain_entry *get_callchain_entry(int *rctx)
 157 {
 158         int cpu;
 159         struct callchain_cpus_entries *entries;
 160
 161         *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
 162         if (*rctx == -1)
 163                 return NULL;
 164
 165         entries = rcu_dereference(callchain_cpus_entries);
 166         if (!entries)
 167                 return NULL;
 168
 169         cpu = smp_processor_id();
 170
 171         return (((void *)entries->cpu_entries[cpu]) +
 172                 (*rctx * perf_callchain_entry__sizeof()));
 173 }
 174
 175 static void
 176 put_callchain_entry(int rctx)
 177 {
 178         put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
 179 }
 180
 181 struct perf_callchain_entry *
 182 perf_callchain(struct perf_event *event, struct pt_regs *regs)
 183 {
 184         bool kernel = !event->attr.exclude_callchain_kernel;
 185         bool user   = !event->attr.exclude_callchain_user;
 186         /* Disallow cross-task user callchains. */
 187         bool crosstask = event->ctx->task && event->ctx->task != current;
 188         const u32 max_stack = event->attr.sample_max_stack;
 189
 190         if (!kernel && !user)
 191                 return NULL;
 192
 193         return get_perf_callchain(regs, 0, kernel, user, max_stack, crosstask, true);
 194 }
 195
 196 struct perf_callchain_entry *
 197 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
 198                    u32 max_stack, bool crosstask, bool add_mark)
 199 {
 200         struct perf_callchain_entry *entry;
 201         struct perf_callchain_entry_ctx ctx;
 202         int rctx;
 203
 204         entry = get_callchain_entry(&rctx);
 205         if (rctx == -1)
 206                 return NULL;
 207
 208         if (!entry)
 209                 goto exit_put;
 210
 211         ctx.entry     = entry;
 212         ctx.max_stack = max_stack;
 213         ctx.nr        = entry->nr = init_nr;
 214         ctx.contexts       = 0;
 215         ctx.contexts_maxed = false;
 216
 217         if (kernel && !user_mode(regs)) {
 218                 if (add_mark)
 219                         perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
 220                 perf_callchain_kernel(&ctx, regs);
 221         }
 222
 223         if (user) {
 224                 if (!user_mode(regs)) {
 225                         if  (current->mm)
 226                                 regs = task_pt_regs(current);
 227                         else
 228                                 regs = NULL;
 229                 }
 230
 231                 if (regs) {
 232                         mm_segment_t fs;
 233
 234                         if (crosstask)
 235                                 goto exit_put;
 236
 237                         if (add_mark)
 238                                 perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
 239
 240                         fs = get_fs();
 241                         set_fs(USER_DS);
 242                         perf_callchain_user(&ctx, regs);
 243                         set_fs(fs);
 244                 }
 245         }
 246
 247 exit_put:
 248         put_callchain_entry(rctx);
 249
 250         return entry;
 251 }
 252
 253 /*
 254  * Used for sysctl_perf_event_max_stack and
 255  * sysctl_perf_event_max_contexts_per_stack.
 256  */
 257 int perf_event_max_stack_handler(struct ctl_table *table, int write,
 258                                  void __user *buffer, size_t *lenp, loff_t *ppos)
 259 {
 260         int *value = table->data;
 261         int new_value = *value, ret;
 262         struct ctl_table new_table = *table;
 263
 264         new_table.data = &new_value;
 265         ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
 266         if (ret || !write)
 267                 return ret;
 268
 269         mutex_lock(&callchain_mutex);
 270         if (atomic_read(&nr_callchain_events))
 271                 ret = -EBUSY;
 272         else
 273                 *value = new_value;
 274
 275         mutex_unlock(&callchain_mutex);
 276
 277         return ret;
 278 }