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