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 int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;
  23
  24 static inline size_t perf_callchain_entry__sizeof(void)
  25 {
  26         return (sizeof(struct perf_callchain_entry) +
  27                 sizeof(__u64) * (sysctl_perf_event_max_stack +
  28                                  sysctl_perf_event_max_contexts_per_stack));
  29 }
  30
  31 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
  32 static atomic_t nr_callchain_events;
  33 static DEFINE_MUTEX(callchain_mutex);
  34 static struct callchain_cpus_entries *callchain_cpus_entries;
  35
  36
  37 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
  38                                   struct pt_regs *regs)
  39 {
  40 }
  41
  42 __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
  43                                 struct pt_regs *regs)
  44 {
  45 }
  46
  47 static void release_callchain_buffers_rcu(struct rcu_head *head)
  48 {
  49         struct callchain_cpus_entries *entries;
  50         int cpu;
  51
  52         entries = container_of(head, struct callchain_cpus_entries, rcu_head);
  53
  54         for_each_possible_cpu(cpu)
  55                 kfree(entries->cpu_entries[cpu]);
  56
  57         kfree(entries);
  58 }
  59
  60 static void release_callchain_buffers(void)
  61 {
  62         struct callchain_cpus_entries *entries;
  63
  64         entries = callchain_cpus_entries;
  65         RCU_INIT_POINTER(callchain_cpus_entries, NULL);
  66         call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
  67 }
  68
  69 static int alloc_callchain_buffers(void)
  70 {
  71         int cpu;
  72         int size;
  73         struct callchain_cpus_entries *entries;
  74
  75         /*
  76          * We can't use the percpu allocation API for data that can be
  77          * accessed from NMI. Use a temporary manual per cpu allocation
  78          * until that gets sorted out.
  79          */
  80         size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
  81
  82         entries = kzalloc(size, GFP_KERNEL);
  83         if (!entries)
  84                 return -ENOMEM;
  85
  86         size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
  87
  88         for_each_possible_cpu(cpu) {
  89                 entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
  90                                                          cpu_to_node(cpu));
  91                 if (!entries->cpu_entries[cpu])
  92                         goto fail;
  93         }
  94
  95         rcu_assign_pointer(callchain_cpus_entries, entries);
  96
  97         return 0;
  98
  99 fail:
 100         for_each_possible_cpu(cpu)
 101                 kfree(entries->cpu_entries[cpu]);
 102         kfree(entries);
 103
 104         return -ENOMEM;
 105 }
 106
 107 int get_callchain_buffers(int event_max_stack)
 108 {
 109         int err = 0;
 110         int count;
 111
 112         mutex_lock(&callchain_mutex);
 113
 114         count = atomic_inc_return(&nr_callchain_events);
 115         if (WARN_ON_ONCE(count < 1)) {
 116                 err = -EINVAL;
 117                 goto exit;
 118         }
 119
 120         if (count > 1) {
 121                 /* If the allocation failed, give up */
 122                 if (!callchain_cpus_entries)
 123                         err = -ENOMEM;
 124                 /*
 125                  * If requesting per event more than the global cap,
 126                  * return a different error to help userspace figure
 127                  * this out.
 128                  *
 129                  * And also do it here so that we have &callchain_mutex held.
 130                  */
 131                 if (event_max_stack > sysctl_perf_event_max_stack)
 132                         err = -EOVERFLOW;
 133                 goto exit;
 134         }
 135
 136         err = alloc_callchain_buffers();
 137 exit:
 138         if (err)
 139                 atomic_dec(&nr_callchain_events);
 140
 141         mutex_unlock(&callchain_mutex);
 142
 143         return err;
 144 }
 145
 146 void put_callchain_buffers(void)
 147 {
 148         if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
 149                 release_callchain_buffers();
 150                 mutex_unlock(&callchain_mutex);
 151         }
 152 }
 153
 154 static struct perf_callchain_entry *get_callchain_entry(int *rctx)
 155 {
 156         int cpu;
 157         struct callchain_cpus_entries *entries;
 158
 159         *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
 160         if (*rctx == -1)
 161                 return NULL;
 162
 163         entries = rcu_dereference(callchain_cpus_entries);
 164         if (!entries)
 165                 return NULL;
 166
 167         cpu = smp_processor_id();
 168
 169         return (((void *)entries->cpu_entries[cpu]) +
 170                 (*rctx * perf_callchain_entry__sizeof()));
 171 }
 172
 173 static void
 174 put_callchain_entry(int rctx)
 175 {
 176         put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
 177 }
 178
 179 struct perf_callchain_entry *
 180 perf_callchain(struct perf_event *event, struct pt_regs *regs)
 181 {
 182         bool kernel = !event->attr.exclude_callchain_kernel;
 183         bool user   = !event->attr.exclude_callchain_user;
 184         /* Disallow cross-task user callchains. */
 185         bool crosstask = event->ctx->task && event->ctx->task != current;
 186         const u32 max_stack = event->attr.sample_max_stack;
 187
 188         if (!kernel && !user)
 189                 return NULL;
 190
 191         return get_perf_callchain(regs, 0, kernel, user, max_stack, crosstask, true);
 192 }
 193
 194 struct perf_callchain_entry *
 195 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
 196                    u32 max_stack, bool crosstask, bool add_mark)
 197 {
 198         struct perf_callchain_entry *entry;
 199         struct perf_callchain_entry_ctx ctx;
 200         int rctx;
 201
 202         entry = get_callchain_entry(&rctx);
 203         if (rctx == -1)
 204                 return NULL;
 205
 206         if (!entry)
 207                 goto exit_put;
 208
 209         ctx.entry     = entry;
 210         ctx.max_stack = max_stack;
 211         ctx.nr        = entry->nr = init_nr;
 212         ctx.contexts       = 0;
 213         ctx.contexts_maxed = false;
 214
 215         if (kernel && !user_mode(regs)) {
 216                 if (add_mark)
 217                         perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
 218                 perf_callchain_kernel(&ctx, regs);
 219         }
 220
 221         if (user) {
 222                 if (!user_mode(regs)) {
 223                         if  (current->mm)
 224                                 regs = task_pt_regs(current);
 225                         else
 226                                 regs = NULL;
 227                 }
 228
 229                 if (regs) {
 230                         if (crosstask)
 231                                 goto exit_put;
 232
 233                         if (add_mark)
 234                                 perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
 235                         perf_callchain_user(&ctx, regs);
 236                 }
 237         }
 238
 239 exit_put:
 240         put_callchain_entry(rctx);
 241
 242         return entry;
 243 }
 244
 245 /*
 246  * Used for sysctl_perf_event_max_stack and
 247  * sysctl_perf_event_max_contexts_per_stack.
 248  */
 249 int perf_event_max_stack_handler(struct ctl_table *table, int write,
 250                                  void __user *buffer, size_t *lenp, loff_t *ppos)
 251 {
 252         int *value = table->data;
 253         int new_value = *value, ret;
 254         struct ctl_table new_table = *table;
 255
 256         new_table.data = &new_value;
 257         ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
 258         if (ret || !write)
 259                 return ret;
 260
 261         mutex_lock(&callchain_mutex);
 262         if (atomic_read(&nr_callchain_events))
 263                 ret = -EBUSY;
 264         else
 265                 *value = new_value;
 266
 267         mutex_unlock(&callchain_mutex);
 268
 269         return ret;
 270 }