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 #include <linux/uprobes.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[];
  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(u8, 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 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                 put_recursion_context(this_cpu_ptr(callchain_recursion), *rctx);
 165                 return NULL;
 166         }
 167
 168         cpu = smp_processor_id();
 169
 170         return (((void *)entries->cpu_entries[cpu]) +
 171                 (*rctx * perf_callchain_entry__sizeof()));
 172 }
 173
 174 void
 175 put_callchain_entry(int rctx)
 176 {
 177         put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
 178 }
 179
 180 static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entry,
 181                                                int start_entry_idx)
 182 {
 183 #ifdef CONFIG_UPROBES
 184         struct uprobe_task *utask = current->utask;
 185         struct return_instance *ri;
 186         __u64 *cur_ip, *last_ip, tramp_addr;
 187
 188         if (likely(!utask || !utask->return_instances))
 189                 return;
 190
 191         cur_ip = &entry->ip[start_entry_idx];
 192         last_ip = &entry->ip[entry->nr - 1];
 193         ri = utask->return_instances;
 194         tramp_addr = uprobe_get_trampoline_vaddr();
 195
 196         /*
 197          * If there are pending uretprobes for the current thread, they are
 198          * recorded in a list inside utask->return_instances; each such
 199          * pending uretprobe replaces traced user function's return address on
 200          * the stack, so when stack trace is captured, instead of seeing
 201          * actual function's return address, we'll have one or many uretprobe
 202          * trampoline addresses in the stack trace, which are not helpful and
 203          * misleading to users.
 204          * So here we go over the pending list of uretprobes, and each
 205          * encountered trampoline address is replaced with actual return
 206          * address.
 207          */
 208         while (ri && cur_ip <= last_ip) {
 209                 if (*cur_ip == tramp_addr) {
 210                         *cur_ip = ri->orig_ret_vaddr;
 211                         ri = ri->next;
 212                 }
 213                 cur_ip++;
 214         }
 215 #endif
 216 }
 217
 218 struct perf_callchain_entry *
 219 get_perf_callchain(struct pt_regs *regs, u32 init_nr, bool kernel, bool user,
 220                    u32 max_stack, bool crosstask, bool add_mark)
 221 {
 222         struct perf_callchain_entry *entry;
 223         struct perf_callchain_entry_ctx ctx;
 224         int rctx, start_entry_idx;
 225
 226         entry = get_callchain_entry(&rctx);
 227         if (!entry)
 228                 return NULL;
 229
 230         ctx.entry     = entry;
 231         ctx.max_stack = max_stack;
 232         ctx.nr        = entry->nr = init_nr;
 233         ctx.contexts       = 0;
 234         ctx.contexts_maxed = false;
 235
 236         if (kernel && !user_mode(regs)) {
 237                 if (add_mark)
 238                         perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
 239                 perf_callchain_kernel(&ctx, regs);
 240         }
 241
 242         if (user) {
 243                 if (!user_mode(regs)) {
 244                         if  (current->mm)
 245                                 regs = task_pt_regs(current);
 246                         else
 247                                 regs = NULL;
 248                 }
 249
 250                 if (regs) {
 251                         if (crosstask)
 252                                 goto exit_put;
 253
 254                         if (add_mark)
 255                                 perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);
 256
 257                         start_entry_idx = entry->nr;
 258                         perf_callchain_user(&ctx, regs);
 259                         fixup_uretprobe_trampoline_entries(entry, start_entry_idx);
 260                 }
 261         }
 262
 263 exit_put:
 264         put_callchain_entry(rctx);
 265
 266         return entry;
 267 }
 268
 269 /*
 270  * Used for sysctl_perf_event_max_stack and
 271  * sysctl_perf_event_max_contexts_per_stack.
 272  */
 273 int perf_event_max_stack_handler(const struct ctl_table *table, int write,
 274                                  void *buffer, size_t *lenp, loff_t *ppos)
 275 {
 276         int *value = table->data;
 277         int new_value = *value, ret;
 278         struct ctl_table new_table = *table;
 279
 280         new_table.data = &new_value;
 281         ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
 282         if (ret || !write)
 283                 return ret;
 284
 285         mutex_lock(&callchain_mutex);
 286         if (atomic_read(&nr_callchain_events))
 287                 ret = -EBUSY;
 288         else
 289                 *value = new_value;
 290
 291         mutex_unlock(&callchain_mutex);
 292
 293         return ret;
 294 }