kernel/events/callchain.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Performance events callchain code, extracted from core.c:
   4  *
   5  *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
   6  *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
   7  *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
   8  *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
   9  */
  10
  11 #include <linux/perf_event.h>
  12 #include <linux/slab.h>
  13 #include <linux/sched/task_stack.h>
  14
  15 #include "internal.h"
  16
  17 struct callchain_cpus_entries {
  18         struct rcu_head                 rcu_head;
  19         struct perf_callchain_entry     *cpu_entries[];
  20 };
  21
  22 int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
  23 int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;
  24
  25 static inline size_t perf_callchain_entry__sizeof(void)
  26 {
  27         return (sizeof(struct perf_callchain_entry) +
  28                 sizeof(__u64) * (sysctl_perf_event_max_stack +
  29                                  sysctl_perf_event_max_contexts_per_stack));
  30 }
  31
  32 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
  33 static atomic_t nr_callchain_events;
  34 static DEFINE_MUTEX(callchain_mutex);
  35 static struct callchain_cpus_entries *callchain_cpus_entries;
  36
  37
  38 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
  39                                   struct pt_regs *regs)
  40 {
  41 }
  42
  43 __weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
  44                                 struct pt_regs *regs)
  45 {
  46 }
  47
  48 static void release_callchain_buffers_rcu(struct rcu_head *head)
  49 {
  50         struct callchain_cpus_entries *entries;
  51         int cpu;
  52
  53         entries = container_of(head, struct callchain_cpus_entries, rcu_head);
  54
  55         for_each_possible_cpu(cpu)
  56                 kfree(entries->cpu_entries[cpu]);
  57
  58         kfree(entries);
  59 }
  60
  61 static void release_callchain_buffers(void)
  62 {
  63         struct callchain_cpus_entries *entries;
  64
  65         entries = callchain_cpus_entries;
  66         RCU_INIT_POINTER(callchain_cpus_entries, NULL);
  67         call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
  68 }
  69
  70 static int alloc_callchain_buffers(void)
  71 {
  72         int cpu;
  73         int size;
  74         struct callchain_cpus_entries *entries;
  75
  76         /*
  77          * We can't use the percpu allocation API for data that can be
  78          * accessed from NMI. Use a temporary manual per cpu allocation
  79          * until that gets sorted out.
  80          */
  81         size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);
  82
  83         entries = kzalloc(size, GFP_KERNEL);
  84         if (!entries)
  85                 return -ENOMEM;
  86
  87         size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;
  88
  89         for_each_possible_cpu(cpu) {
  90                 entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
  91                                                          cpu_to_node(cpu));
  92                 if (!entries->cpu_entries[cpu])
  93                         goto fail;
  94         }
  95
  96         rcu_assign_pointer(callchain_cpus_entries, entries);
  97
  98         return 0;
  99
 100 fail:
 101         for_each_possible_cpu(cpu)
 102                 kfree(entries->cpu_entries[cpu]);
 103         kfree(entries);
 104
 105         return -ENOMEM;
 106 }
 107
 108 int get_callchain_buffers(int event_max_stack)
 109 {
 110         int err = 0;
 111         int count;
 112
 113         mutex_lock(&callchain_mutex);
 114
 115         count = atomic_inc_return(&nr_callchain_events);
 116         if (WARN_ON_ONCE(count < 1)) {
 117                 err = -EINVAL;
 118                 goto exit;
 119         }
 120
 121         /*
 122          * If requesting per event more than the global cap,
 123          * return a different error to help userspace figure
 124          * this out.
 125          *
 126          * And also do it here so that we have &callchain_mutex held.
 127          */
 128         if (event_max_stack > sysctl_perf_event_max_stack) {
 129                 err = -EOVERFLOW;
 130                 goto exit;
 131         }
 132
 133         if (count == 1)
 134                 err = alloc_callchain_buffers();
 135 exit:
 136         if (err)
 137                 atomic_dec(&nr_callchain_events);
 138
 139         mutex_unlock(&callchain_mutex);
 140
 141         return err;
 142 }
 143
 144 void put_callchain_buffers(void)
 145 {
 146         if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
 147                 release_callchain_buffers();
 148                 mutex_unlock(&callchain_mutex);
 149         }
 150 }
 151
 152 struct perf_callchain_entry *get_callchain_entry(int *rctx)
 153 {
 154         int cpu;
 155         struct callchain_cpus_entries *entries;
 156
 157         *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
 158         if (*rctx == -1)
 159                 return NULL;
 160
 161         entries = rcu_dereference(callchain_cpus_entries);
 162         if (!entries) {
 163                 put_recursion_context(this_cpu_ptr(callchain_recursion), *rctx);
 164                 return NULL;
 165         }
 166
 167         cpu = smp_processor_id();
 168
 169         return (((void *)entries->cpu_entries[cpu]) +
 170                 (*rctx * perf_callchain_entry__sizeof()));
 171 }
 172
 173 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 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
 181                    u32 max_stack, bool crosstask, bool add_mark)
 182 {
 183         struct perf_callchain_entry *entry;
 184         struct perf_callchain_entry_ctx ctx;
 185         int rctx;
 186
 187         entry = get_callchain_entry(&rctx);
 188         if (!entry)
 189                 return NULL;
 190
 191         ctx.entry     = entry;
 192         ctx.max_stack = max_stack;
 193         ctx.nr        = entry->nr = init_nr;
 194         ctx.contexts       = 0;
 195         ctx.contexts_maxed = false;
 196
 197         if (kernel && !user_mode(regs)) {
 198                 if (add_mark)
 199                         perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
 200                 perf_callchain_kernel(&ctx, regs);
 201         }
 202
 203         if (user) {
 204                 if (!user_mode(regs)) {
 205                         if  (current->mm)
 206                                 regs = task_pt_regs(current);
 207                         else
 208                                 regs = NULL;
 209                 }
 210
 211                 if (regs) {
 212                         mm_segment_t fs;
 213
 214                         if (crosstask)
 215                                 goto exit_put;
 216
 217                         if (add_mark)
 218                                 perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
 219
 220                         fs = force_uaccess_begin();
 221                         perf_callchain_user(&ctx, regs);
 222                         force_uaccess_end(fs);
 223                 }
 224         }
 225
 226 exit_put:
 227         put_callchain_entry(rctx);
 228
 229         return entry;
 230 }
 231
 232 /*
 233  * Used for sysctl_perf_event_max_stack and
 234  * sysctl_perf_event_max_contexts_per_stack.
 235  */
 236 int perf_event_max_stack_handler(struct ctl_table *table, int write,
 237                                  void *buffer, size_t *lenp, loff_t *ppos)
 238 {
 239         int *value = table->data;
 240         int new_value = *value, ret;
 241         struct ctl_table new_table = *table;
 242
 243         new_table.data = &new_value;
 244         ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
 245         if (ret || !write)
 246                 return ret;
 247
 248         mutex_lock(&callchain_mutex);
 249         if (atomic_read(&nr_callchain_events))
 250                 ret = -EBUSY;
 251         else
 252                 *value = new_value;
 253
 254         mutex_unlock(&callchain_mutex);
 255
 256         return ret;
 257 }