kernel/trace/trace_stack.c

   1 /*
   2  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
   3  *
   4  */
   5 #include <linux/stacktrace.h>
   6 #include <linux/kallsyms.h>
   7 #include <linux/seq_file.h>
   8 #include <linux/spinlock.h>
   9 #include <linux/uaccess.h>
  10 #include <linux/debugfs.h>
  11 #include <linux/ftrace.h>
  12 #include <linux/module.h>
  13 #include <linux/sysctl.h>
  14 #include <linux/init.h>
  15 #include <linux/fs.h>
  16 #include "trace.h"
  17
  18 #define STACK_TRACE_ENTRIES 500
  19
  20 #ifdef CC_USING_FENTRY
  21 # define fentry         1
  22 #else
  23 # define fentry         0
  24 #endif
  25
  26 static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
  27          { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
  28 static unsigned stack_dump_index[STACK_TRACE_ENTRIES];
  29
  30 /*
  31  * Reserve one entry for the passed in ip. This will allow
  32  * us to remove most or all of the stack size overhead
  33  * added by the stack tracer itself.
  34  */
  35 static struct stack_trace max_stack_trace = {
  36         .max_entries            = STACK_TRACE_ENTRIES - 1,
  37         .entries                = &stack_dump_trace[1],
  38 };
  39
  40 static unsigned long max_stack_size;
  41 static arch_spinlock_t max_stack_lock =
  42         (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
  43
  44 static int stack_trace_disabled __read_mostly;
  45 static DEFINE_PER_CPU(int, trace_active);
  46 static DEFINE_MUTEX(stack_sysctl_mutex);
  47
  48 int stack_tracer_enabled;
  49 static int last_stack_tracer_enabled;
  50
  51 static inline void
  52 check_stack(unsigned long ip, unsigned long *stack)
  53 {
  54         unsigned long this_size, flags;
  55         unsigned long *p, *top, *start;
  56         static int tracer_frame;
  57         int frame_size = ACCESS_ONCE(tracer_frame);
  58         int i;
  59
  60         this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
  61         this_size = THREAD_SIZE - this_size;
  62         /* Remove the frame of the tracer */
  63         this_size -= frame_size;
  64
  65         if (this_size <= max_stack_size)
  66                 return;
  67
  68         /* we do not handle interrupt stacks yet */
  69         if (!object_is_on_stack(stack))
  70                 return;
  71
  72         local_irq_save(flags);
  73         arch_spin_lock(&max_stack_lock);
  74
  75         /* In case another CPU set the tracer_frame on us */
  76         if (unlikely(!frame_size))
  77                 this_size -= tracer_frame;
  78
  79         /* a race could have already updated it */
  80         if (this_size <= max_stack_size)
  81                 goto out;
  82
  83         max_stack_size = this_size;
  84
  85         max_stack_trace.nr_entries      = 0;
  86         max_stack_trace.skip            = 3;
  87
  88         save_stack_trace(&max_stack_trace);
  89
  90         /*
  91          * Add the passed in ip from the function tracer.
  92          * Searching for this on the stack will skip over
  93          * most of the overhead from the stack tracer itself.
  94          */
  95         stack_dump_trace[0] = ip;
  96         max_stack_trace.nr_entries++;
  97
  98         /*
  99          * Now find where in the stack these are.
 100          */
 101         i = 0;
 102         start = stack;
 103         top = (unsigned long *)
 104                 (((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);
 105
 106         /*
 107          * Loop through all the entries. One of the entries may
 108          * for some reason be missed on the stack, so we may
 109          * have to account for them. If they are all there, this
 110          * loop will only happen once. This code only takes place
 111          * on a new max, so it is far from a fast path.
 112          */
 113         while (i < max_stack_trace.nr_entries) {
 114                 int found = 0;
 115
 116                 stack_dump_index[i] = this_size;
 117                 p = start;
 118
 119                 for (; p < top && i < max_stack_trace.nr_entries; p++) {
 120                         if (*p == stack_dump_trace[i]) {
 121                                 this_size = stack_dump_index[i++] =
 122                                         (top - p) * sizeof(unsigned long);
 123                                 found = 1;
 124                                 /* Start the search from here */
 125                                 start = p + 1;
 126                                 /*
 127                                  * We do not want to show the overhead
 128                                  * of the stack tracer stack in the
 129                                  * max stack. If we haven't figured
 130                                  * out what that is, then figure it out
 131                                  * now.
 132                                  */
 133                                 if (unlikely(!tracer_frame) && i == 1) {
 134                                         tracer_frame = (p - stack) *
 135                                                 sizeof(unsigned long);
 136                                         max_stack_size -= tracer_frame;
 137                                 }
 138                         }
 139                 }
 140
 141                 if (!found)
 142                         i++;
 143         }
 144
 145  out:
 146         arch_spin_unlock(&max_stack_lock);
 147         local_irq_restore(flags);
 148 }
 149
 150 static void
 151 stack_trace_call(unsigned long ip, unsigned long parent_ip)
 152 {
 153         unsigned long stack;
 154         int cpu;
 155
 156         if (unlikely(!ftrace_enabled || stack_trace_disabled))
 157                 return;
 158
 159         preempt_disable_notrace();
 160
 161         cpu = raw_smp_processor_id();
 162         /* no atomic needed, we only modify this variable by this cpu */
 163         if (per_cpu(trace_active, cpu)++ != 0)
 164                 goto out;
 165
 166         /*
 167          * When fentry is used, the traced function does not get
 168          * its stack frame set up, and we lose the parent.
 169          * The ip is pretty useless because the function tracer
 170          * was called before that function set up its stack frame.
 171          * In this case, we use the parent ip.
 172          *
 173          * By adding the return address of either the parent ip
 174          * or the current ip we can disregard most of the stack usage
 175          * caused by the stack tracer itself.
 176          *
 177          * The function tracer always reports the address of where the
 178          * mcount call was, but the stack will hold the return address.
 179          */
 180         if (fentry)
 181                 ip = parent_ip;
 182         else
 183                 ip += MCOUNT_INSN_SIZE;
 184
 185         check_stack(ip, &stack);
 186
 187  out:
 188         per_cpu(trace_active, cpu)--;
 189         /* prevent recursion in schedule */
 190         preempt_enable_notrace();
 191 }
 192
 193 static struct ftrace_ops trace_ops __read_mostly =
 194 {
 195         .func = stack_trace_call,
 196         .flags = FTRACE_OPS_FL_GLOBAL,
 197 };
 198
 199 static ssize_t
 200 stack_max_size_read(struct file *filp, char __user *ubuf,
 201                     size_t count, loff_t *ppos)
 202 {
 203         unsigned long *ptr = filp->private_data;
 204         char buf[64];
 205         int r;
 206
 207         r = snprintf(buf, sizeof(buf), "%ld\n", *ptr);
 208         if (r > sizeof(buf))
 209                 r = sizeof(buf);
 210         return simple_read_from_buffer(ubuf, count, ppos, buf, r);
 211 }
 212
 213 static ssize_t
 214 stack_max_size_write(struct file *filp, const char __user *ubuf,
 215                      size_t count, loff_t *ppos)
 216 {
 217         long *ptr = filp->private_data;
 218         unsigned long val, flags;
 219         int ret;
 220         int cpu;
 221
 222         ret = kstrtoul_from_user(ubuf, count, 10, &val);
 223         if (ret)
 224                 return ret;
 225
 226         local_irq_save(flags);
 227
 228         /*
 229          * In case we trace inside arch_spin_lock() or after (NMI),
 230          * we will cause circular lock, so we also need to increase
 231          * the percpu trace_active here.
 232          */
 233         cpu = smp_processor_id();
 234         per_cpu(trace_active, cpu)++;
 235
 236         arch_spin_lock(&max_stack_lock);
 237         *ptr = val;
 238         arch_spin_unlock(&max_stack_lock);
 239
 240         per_cpu(trace_active, cpu)--;
 241         local_irq_restore(flags);
 242
 243         return count;
 244 }
 245
 246 static const struct file_operations stack_max_size_fops = {
 247         .open           = tracing_open_generic,
 248         .read           = stack_max_size_read,
 249         .write          = stack_max_size_write,
 250         .llseek         = default_llseek,
 251 };
 252
 253 static void *
 254 __next(struct seq_file *m, loff_t *pos)
 255 {
 256         long n = *pos - 1;
 257
 258         if (n >= max_stack_trace.nr_entries || stack_dump_trace[n] == ULONG_MAX)
 259                 return NULL;
 260
 261         m->private = (void *)n;
 262         return &m->private;
 263 }
 264
 265 static void *
 266 t_next(struct seq_file *m, void *v, loff_t *pos)
 267 {
 268         (*pos)++;
 269         return __next(m, pos);
 270 }
 271
 272 static void *t_start(struct seq_file *m, loff_t *pos)
 273 {
 274         int cpu;
 275
 276         local_irq_disable();
 277
 278         cpu = smp_processor_id();
 279         per_cpu(trace_active, cpu)++;
 280
 281         arch_spin_lock(&max_stack_lock);
 282
 283         if (*pos == 0)
 284                 return SEQ_START_TOKEN;
 285
 286         return __next(m, pos);
 287 }
 288
 289 static void t_stop(struct seq_file *m, void *p)
 290 {
 291         int cpu;
 292
 293         arch_spin_unlock(&max_stack_lock);
 294
 295         cpu = smp_processor_id();
 296         per_cpu(trace_active, cpu)--;
 297
 298         local_irq_enable();
 299 }
 300
 301 static int trace_lookup_stack(struct seq_file *m, long i)
 302 {
 303         unsigned long addr = stack_dump_trace[i];
 304
 305         return seq_printf(m, "%pS\n", (void *)addr);
 306 }
 307
 308 static void print_disabled(struct seq_file *m)
 309 {
 310         seq_puts(m, "#\n"
 311                  "#  Stack tracer disabled\n"
 312                  "#\n"
 313                  "# To enable the stack tracer, either add 'stacktrace' to the\n"
 314                  "# kernel command line\n"
 315                  "# or 'echo 1 > /proc/sys/kernel/stack_tracer_enabled'\n"
 316                  "#\n");
 317 }
 318
 319 static int t_show(struct seq_file *m, void *v)
 320 {
 321         long i;
 322         int size;
 323
 324         if (v == SEQ_START_TOKEN) {
 325                 seq_printf(m, "        Depth    Size   Location"
 326                            "    (%d entries)\n"
 327                            "        -----    ----   --------\n",
 328                            max_stack_trace.nr_entries - 1);
 329
 330                 if (!stack_tracer_enabled && !max_stack_size)
 331                         print_disabled(m);
 332
 333                 return 0;
 334         }
 335
 336         i = *(long *)v;
 337
 338         if (i >= max_stack_trace.nr_entries ||
 339             stack_dump_trace[i] == ULONG_MAX)
 340                 return 0;
 341
 342         if (i+1 == max_stack_trace.nr_entries ||
 343             stack_dump_trace[i+1] == ULONG_MAX)
 344                 size = stack_dump_index[i];
 345         else
 346                 size = stack_dump_index[i] - stack_dump_index[i+1];
 347
 348         seq_printf(m, "%3ld) %8d   %5d   ", i, stack_dump_index[i], size);
 349
 350         trace_lookup_stack(m, i);
 351
 352         return 0;
 353 }
 354
 355 static const struct seq_operations stack_trace_seq_ops = {
 356         .start          = t_start,
 357         .next           = t_next,
 358         .stop           = t_stop,
 359         .show           = t_show,
 360 };
 361
 362 static int stack_trace_open(struct inode *inode, struct file *file)
 363 {
 364         return seq_open(file, &stack_trace_seq_ops);
 365 }
 366
 367 static const struct file_operations stack_trace_fops = {
 368         .open           = stack_trace_open,
 369         .read           = seq_read,
 370         .llseek         = seq_lseek,
 371         .release        = seq_release,
 372 };
 373
 374 int
 375 stack_trace_sysctl(struct ctl_table *table, int write,
 376                    void __user *buffer, size_t *lenp,
 377                    loff_t *ppos)
 378 {
 379         int ret;
 380
 381         mutex_lock(&stack_sysctl_mutex);
 382
 383         ret = proc_dointvec(table, write, buffer, lenp, ppos);
 384
 385         if (ret || !write ||
 386             (last_stack_tracer_enabled == !!stack_tracer_enabled))
 387                 goto out;
 388
 389         last_stack_tracer_enabled = !!stack_tracer_enabled;
 390
 391         if (stack_tracer_enabled)
 392                 register_ftrace_function(&trace_ops);
 393         else
 394                 unregister_ftrace_function(&trace_ops);
 395
 396  out:
 397         mutex_unlock(&stack_sysctl_mutex);
 398         return ret;
 399 }
 400
 401 static __init int enable_stacktrace(char *str)
 402 {
 403         stack_tracer_enabled = 1;
 404         last_stack_tracer_enabled = 1;
 405         return 1;
 406 }
 407 __setup("stacktrace", enable_stacktrace);
 408
 409 static __init int stack_trace_init(void)
 410 {
 411         struct dentry *d_tracer;
 412
 413         d_tracer = tracing_init_dentry();
 414         if (!d_tracer)
 415                 return 0;
 416
 417         trace_create_file("stack_max_size", 0644, d_tracer,
 418                         &max_stack_size, &stack_max_size_fops);
 419
 420         trace_create_file("stack_trace", 0444, d_tracer,
 421                         NULL, &stack_trace_fops);
 422
 423         if (stack_tracer_enabled)
 424                 register_ftrace_function(&trace_ops);
 425
 426         return 0;
 427 }
 428
 429 device_initcall(stack_trace_init);