ltt-usertrace/ltt-usertrace-fast.c

   1 /* LTTng user-space "fast" library
   2  *
   3  * This daemon is spawned by each traced thread (to share the mmap).
   4  *
   5  * Its job is to dump periodically this buffer to disk (when it receives a
   6  * SIGUSR1 from its parent).
   7  *
   8  * It uses the control information in the shared memory area (producer/consumer
   9  * count).
  10  *
  11  * When the parent thread dies (yes, those thing may happen) ;) , this daemon
  12  * will flush the last buffer and write it to disk.
  13  *
  14  * Supplement note for streaming : the daemon is responsible for flushing
  15  * periodically the buffer if it is streaming data.
  16  *
  17  *
  18  * Notes :
  19  * shm memory is typically limited to 4096 units (system wide limit SHMMNI in
  20  * /proc/sys/kernel/shmmni). As it requires computation time upon creation, we
  21  * do not use it : we will use a shared mmap() instead which is passed through
  22  * the fork().
  23  * MAP_SHARED mmap segment. Updated when msync or munmap are called.
  24  * MAP_ANONYMOUS.
  25  * Memory  mapped  by  mmap()  is  preserved across fork(2), with the same
  26  *   attributes.
  27  *
  28  * Eventually, there will be two mode :
  29  * * Slow thread spawn : a fork() is done for each new thread. If the process
  30  *   dies, the data is not lost.
  31  * * Fast thread spawn : a pthread_create() is done by the application for each
  32  *   new thread.
  33  *
  34  * We use a timer to check periodically if the parent died. I think it is less
  35  * intrusive than a ptrace() on the parent, which would get every signal. The
  36  * side effect of this is that we won't be notified if the parent does an
  37  * exec(). In this case, we will just sit there until the parent exits.
  38  *
  39  *
  40  * Copyright 2006 Mathieu Desnoyers
  41  *
  42  */
  43
  44 #define inline inline __attribute__((always_inline))
  45
  46 #define _GNU_SOURCE
  47 #define LTT_TRACE
  48 #define LTT_TRACE_FAST
  49 #include <sys/types.h>
  50 #include <sys/wait.h>
  51 #include <unistd.h>
  52 #include <stdlib.h>
  53 #include <stdio.h>
  54 #include <signal.h>
  55 #include <syscall.h>
  56 #include <features.h>
  57 #include <pthread.h>
  58 #include <malloc.h>
  59 #include <string.h>
  60 #include <sys/mman.h>
  61 #include <signal.h>
  62 #include <sys/stat.h>
  63 #include <fcntl.h>
  64 #include <stdlib.h>
  65 #include <sys/param.h>
  66 #include <sys/time.h>
  67 #include <errno.h>
  68
  69 #include <asm/atomic.h>
  70 #include <asm/timex.h>  //for get_cycles()
  71
  72 _syscall0(pid_t,gettid)
  73
  74 #include <ltt/ltt-usertrace.h>
  75
  76 #ifdef LTT_SHOW_DEBUG
  77 #define dbg_printf(...) printf(__VA_ARGS__)
  78 #else
  79 #define dbg_printf(...)
  80 #endif //LTT_SHOW_DEBUG
  81
  82
  83 enum force_switch_mode { FORCE_ACTIVE, FORCE_FLUSH };
  84
  85 /* Writer (the traced application) */
  86
  87 __thread struct ltt_trace_info *thread_trace_info = NULL;
  88
  89 void ltt_usertrace_fast_buffer_switch(void)
  90 {
  91         struct ltt_trace_info *tmp = thread_trace_info;
  92         if(tmp)
  93                 kill(tmp->daemon_id, SIGUSR1);
  94 }
  95
  96 /* The cleanup should never be called from a signal handler */
  97 static void ltt_usertrace_fast_cleanup(void *arg)
  98 {
  99         struct ltt_trace_info *tmp = thread_trace_info;
 100         if(tmp) {
 101                 thread_trace_info = NULL;
 102                 kill(tmp->daemon_id, SIGUSR2);
 103                 munmap(tmp, sizeof(*tmp));
 104         }
 105 }
 106
 107 /* Reader (the disk dumper daemon) */
 108
 109 static pid_t traced_pid = 0;
 110 static pid_t traced_tid = 0;
 111 static int parent_exited = 0;
 112 static int fd_process = -1;
 113 static char outfile_name[PATH_MAX];
 114 static char identifier_name[PATH_MAX];
 115
 116 /* signal handling */
 117 static void handler_sigusr1(int signo)
 118 {
 119         dbg_printf("LTT Signal %d received : parent buffer switch.\n", signo);
 120 }
 121
 122 static void handler_sigusr2(int signo)
 123 {
 124         dbg_printf("LTT Signal %d received : parent exited.\n", signo);
 125         parent_exited = 1;
 126 }
 127
 128 static void handler_sigalarm(int signo)
 129 {
 130         dbg_printf("LTT Signal %d received\n", signo);
 131
 132         if(getppid() != traced_pid) {
 133                 /* Parent died */
 134                 dbg_printf("LTT Parent %lu died, cleaning up\n", traced_pid);
 135                 traced_pid = 0;
 136         }
 137         alarm(3);
 138 }
 139
 140 /* Do a buffer switch. Don't switch if buffer is completely empty */
 141 static void flush_buffer(struct ltt_buf *ltt_buf, enum force_switch_mode mode)
 142 {
 143         uint64_t tsc;
 144         int offset_begin, offset_end, offset_old;
 145         int reserve_commit_diff;
 146         int consumed_old, consumed_new;
 147         int commit_count, reserve_count;
 148         int end_switch_old;
 149
 150         do {
 151                 offset_old = atomic_read(&ltt_buf->offset);
 152                 offset_begin = offset_old;
 153                 end_switch_old = 0;
 154                 tsc = ltt_get_timestamp();
 155                 if(tsc == 0) {
 156                         /* Error in getting the timestamp : should not happen : it would
 157                          * mean we are called from an NMI during a write seqlock on xtime. */
 158                         return;
 159                 }
 160
 161                 if(SUBBUF_OFFSET(offset_begin, ltt_buf) != 0) {
 162                         offset_begin = SUBBUF_ALIGN(offset_begin, ltt_buf);
 163                         end_switch_old = 1;
 164                 } else {
 165       /* we do not have to switch : buffer is empty */
 166       return;
 167     }
 168                 if(mode == FORCE_ACTIVE)
 169                         offset_begin += ltt_subbuf_header_len(ltt_buf);
 170                 /* Always begin_switch in FORCE_ACTIVE mode */
 171
 172                 /* Test new buffer integrity */
 173                 reserve_commit_diff =
 174                         atomic_read(
 175                                 &ltt_buf->reserve_count[SUBBUF_INDEX(offset_begin, ltt_buf)])
 176                         - atomic_read(
 177                                         &ltt_buf->commit_count[SUBBUF_INDEX(offset_begin, ltt_buf)]);
 178                 if(reserve_commit_diff == 0) {
 179       /* Next buffer not corrupted. */
 180       if(mode == FORCE_ACTIVE
 181                                 && (offset_begin-atomic_read(&ltt_buf->consumed))
 182                                                                                         >= ltt_buf->alloc_size) {
 183         /* We do not overwrite non consumed buffers and we are full : ignore
 184                  switch while tracing is active. */
 185         return;
 186       }
 187     } else {
 188       /* Next subbuffer corrupted. Force pushing reader even in normal mode */
 189     }
 190
 191                 offset_end = offset_begin;
 192         } while(atomic_cmpxchg(&ltt_buf->offset, offset_old, offset_end)
 193                                                         != offset_old);
 194
 195
 196         if(mode == FORCE_ACTIVE) {
 197                 /* Push the reader if necessary */
 198                 do {
 199                         consumed_old = atomic_read(&ltt_buf->consumed);
 200                         /* If buffer is in overwrite mode, push the reader consumed count if
 201                                  the write position has reached it and we are not at the first
 202                                  iteration (don't push the reader farther than the writer).
 203                                  This operation can be done concurrently by many writers in the
 204                                  same buffer, the writer being at the fartest write position sub-buffer
 205                                  index in the buffer being the one which will win this loop. */
 206                         /* If the buffer is not in overwrite mode, pushing the reader only
 207                                  happen if a sub-buffer is corrupted */
 208                         if((SUBBUF_TRUNC(offset_end, ltt_buf)
 209                                         - SUBBUF_TRUNC(consumed_old, ltt_buf))
 210                                                         >= ltt_buf->alloc_size)
 211                                 consumed_new = SUBBUF_ALIGN(consumed_old, ltt_buf);
 212                         else {
 213                                 consumed_new = consumed_old;
 214                                 break;
 215                         }
 216                 } while(atomic_cmpxchg(&ltt_buf->consumed, consumed_old, consumed_new)
 217                                 != consumed_old);
 218
 219                 if(consumed_old != consumed_new) {
 220                         /* Reader pushed : we are the winner of the push, we can therefore
 221                                  reequilibrate reserve and commit. Atomic increment of the commit
 222                                  count permits other writers to play around with this variable
 223                                  before us. We keep track of corrupted_subbuffers even in overwrite
 224                                  mode :
 225                                  we never want to write over a non completely committed sub-buffer :
 226                                  possible causes : the buffer size is too low compared to the unordered
 227                                  data input, or there is a writer who died between the reserve and the
 228                                  commit. */
 229                         if(reserve_commit_diff) {
 230                                 /* We have to alter the sub-buffer commit count : a sub-buffer is
 231                                          corrupted */
 232                                 atomic_add(reserve_commit_diff,
 233                                                                 &ltt_buf->commit_count[SUBBUF_INDEX(offset_begin, ltt_buf)]);
 234                                 atomic_inc(&ltt_buf->corrupted_subbuffers);
 235                         }
 236                 }
 237         }
 238
 239         /* Always switch */
 240
 241         if(end_switch_old) {
 242                 /* old subbuffer */
 243                 /* Concurrency safe because we are the last and only thread to alter this
 244                          sub-buffer. As long as it is not delivered and read, no other thread can
 245                          alter the offset, alter the reserve_count or call the
 246                          client_buffer_end_callback on this sub-buffer.
 247                          The only remaining threads could be the ones with pending commits. They
 248                          will have to do the deliver themself.
 249                          Not concurrency safe in overwrite mode. We detect corrupted subbuffers with
 250                          commit and reserve counts. We keep a corrupted sub-buffers count and push
 251                          the readers across these sub-buffers.
 252                          Not concurrency safe if a writer is stalled in a subbuffer and
 253                          another writer switches in, finding out it's corrupted. The result will be
 254                          than the old (uncommited) subbuffer will be declared corrupted, and that
 255                          the new subbuffer will be declared corrupted too because of the commit
 256                          count adjustment.
 257                          Offset old should never be 0. */
 258                 ltt_buffer_end_callback(ltt_buf, tsc, offset_old,
 259                                 SUBBUF_INDEX((offset_old), ltt_buf));
 260                 /* Setting this reserve_count will allow the sub-buffer to be delivered by
 261                          the last committer. */
 262                 reserve_count = atomic_add_return((SUBBUF_OFFSET((offset_old-1),
 263                                                       ltt_buf) + 1),
 264                                                                                 &ltt_buf->reserve_count[SUBBUF_INDEX((offset_old),
 265                                                           ltt_buf)]);
 266                 if(reserve_count == atomic_read(
 267                                 &ltt_buf->commit_count[SUBBUF_INDEX((offset_old), ltt_buf)])) {
 268                         ltt_deliver_callback(ltt_buf, SUBBUF_INDEX((offset_old), ltt_buf), NULL);
 269                 }
 270         }
 271
 272         if(mode == FORCE_ACTIVE) {
 273                 /* New sub-buffer */
 274                 /* This code can be executed unordered : writers may already have written
 275                          to the sub-buffer before this code gets executed, caution. */
 276                 /* The commit makes sure that this code is executed before the deliver
 277                          of this sub-buffer */
 278                 ltt_buffer_begin_callback(ltt_buf, tsc, SUBBUF_INDEX(offset_begin, ltt_buf));
 279                 commit_count = atomic_add_return(ltt_subbuf_header_len(ltt_buf),
 280                                                                  &ltt_buf->commit_count[SUBBUF_INDEX(offset_begin, ltt_buf)]);
 281                 /* Check if the written buffer has to be delivered */
 282                 if(commit_count == atomic_read(
 283                                         &ltt_buf->reserve_count[SUBBUF_INDEX(offset_begin, ltt_buf)])) {
 284                         ltt_deliver_callback(ltt_buf, SUBBUF_INDEX(offset_begin, ltt_buf), NULL);
 285                 }
 286         }
 287
 288 }
 289
 290
 291 static int open_output_files(void)
 292 {
 293         int ret;
 294         int fd;
 295         /* Open output files */
 296         umask(00000);
 297         ret = mkdir(LTT_USERTRACE_ROOT, 0777);
 298         if(ret < 0 && errno != EEXIST) {
 299                 perror("LTT Error in creating output (mkdir)");
 300                 exit(-1);
 301         }
 302         ret = chdir(LTT_USERTRACE_ROOT);
 303         if(ret < 0) {
 304                 perror("LTT Error in creating output (chdir)");
 305                 exit(-1);
 306         }
 307         snprintf(identifier_name, PATH_MAX-1,   "%lu.%lu.%llu",
 308                         traced_tid, traced_pid, get_cycles());
 309         snprintf(outfile_name, PATH_MAX-1,      "process-%s", identifier_name);
 310
 311 #ifndef LTT_NULL_OUTPUT_TEST
 312         fd = creat(outfile_name, 0644);
 313 #else
 314         /* NULL test */
 315         ret = symlink("/dev/null", outfile_name);
 316         if(ret < 0) {
 317                 perror("error in symlink");
 318                 exit(-1);
 319         }
 320         fd = open(outfile_name, O_WRONLY);
 321         if(fd_process < 0) {
 322                 perror("Error in open");
 323                 exit(-1);
 324         }
 325 #endif //LTT_NULL_OUTPUT_TEST
 326         return fd;
 327 }
 328
 329 static inline int ltt_buffer_get(struct ltt_buf *ltt_buf,
 330                 unsigned int *offset)
 331 {
 332         unsigned int consumed_old, consumed_idx;
 333         consumed_old = atomic_read(&ltt_buf->consumed);
 334         consumed_idx = SUBBUF_INDEX(consumed_old, ltt_buf);
 335
 336         if(atomic_read(&ltt_buf->commit_count[consumed_idx])
 337                 != atomic_read(&ltt_buf->reserve_count[consumed_idx])) {
 338                 return -EAGAIN;
 339         }
 340         if((SUBBUF_TRUNC(atomic_read(&ltt_buf->offset), ltt_buf)
 341                                 -SUBBUF_TRUNC(consumed_old, ltt_buf)) == 0) {
 342                 return -EAGAIN;
 343         }
 344
 345         *offset = consumed_old;
 346
 347         return 0;
 348 }
 349
 350 static inline int ltt_buffer_put(struct ltt_buf *ltt_buf,
 351                 unsigned int offset)
 352 {
 353         unsigned int consumed_old, consumed_new;
 354         int ret;
 355
 356         consumed_old = offset;
 357         consumed_new = SUBBUF_ALIGN(consumed_old, ltt_buf);
 358         if(atomic_cmpxchg(&ltt_buf->consumed, consumed_old, consumed_new)
 359                         != consumed_old) {
 360                 /* We have been pushed by the writer : the last buffer read _is_
 361                  * corrupted!
 362                  * It can also happen if this is a buffer we never got. */
 363                 return -EIO;
 364         } else {
 365                 if(traced_pid == 0 || parent_exited) return 0;
 366
 367                 ret = sem_post(&ltt_buf->writer_sem);
 368                 if(ret < 0) {
 369                         printf("error in sem_post");
 370                 }
 371         }
 372 }
 373
 374 static int read_subbuffer(struct ltt_buf *ltt_buf, int fd)
 375 {
 376         unsigned int consumed_old;
 377         int err;
 378         dbg_printf("LTT read buffer\n");
 379
 380
 381         err = ltt_buffer_get(ltt_buf, &consumed_old);
 382         if(err != 0) {
 383                 if(err != -EAGAIN) dbg_printf("LTT Reserving sub buffer failed\n");
 384                 goto get_error;
 385         }
 386         if(fd_process == -1) {
 387                 fd_process = fd = open_output_files();
 388         }
 389
 390         err = TEMP_FAILURE_RETRY(write(fd,
 391                                 ltt_buf->start
 392                                         + (consumed_old & ((ltt_buf->alloc_size)-1)),
 393                                 ltt_buf->subbuf_size));
 394
 395         if(err < 0) {
 396                 perror("Error in writing to file");
 397                 goto write_error;
 398         }
 399 #if 0
 400         err = fsync(pair->trace);
 401         if(err < 0) {
 402                 ret = errno;
 403                 perror("Error in writing to file");
 404                 goto write_error;
 405         }
 406 #endif //0
 407 write_error:
 408         err = ltt_buffer_put(ltt_buf, consumed_old);
 409
 410         if(err != 0) {
 411                 if(err == -EIO) {
 412                         dbg_printf("Reader has been pushed by the writer, last subbuffer corrupted.\n");
 413                         /* FIXME : we may delete the last written buffer if we wish. */
 414                 }
 415                 goto get_error;
 416         }
 417
 418 get_error:
 419         return err;
 420 }
 421
 422 /* This function is called by ltt_rw_init which has signals blocked */
 423 static void ltt_usertrace_fast_daemon(struct ltt_trace_info *shared_trace_info,
 424                 sigset_t oldset, pid_t l_traced_pid, pthread_t l_traced_tid)
 425 {
 426         struct sigaction act;
 427         int ret;
 428
 429         traced_pid = l_traced_pid;
 430         traced_tid = l_traced_tid;
 431
 432         dbg_printf("LTT ltt_usertrace_fast_daemon : init is %d, pid is %lu, traced_pid is %lu, traced_tid is %lu\n",
 433                         shared_trace_info->init, getpid(), traced_pid, traced_tid);
 434
 435         act.sa_handler = handler_sigusr1;
 436         act.sa_flags = 0;
 437         sigemptyset(&(act.sa_mask));
 438         sigaddset(&(act.sa_mask), SIGUSR1);
 439         sigaction(SIGUSR1, &act, NULL);
 440
 441         act.sa_handler = handler_sigusr2;
 442         act.sa_flags = 0;
 443         sigemptyset(&(act.sa_mask));
 444         sigaddset(&(act.sa_mask), SIGUSR2);
 445         sigaction(SIGUSR2, &act, NULL);
 446
 447         act.sa_handler = handler_sigalarm;
 448         act.sa_flags = 0;
 449         sigemptyset(&(act.sa_mask));
 450         sigaddset(&(act.sa_mask), SIGALRM);
 451         sigaction(SIGALRM, &act, NULL);
 452
 453         alarm(3);
 454
 455         while(1) {
 456                 ret = sigsuspend(&oldset);
 457                 if(ret != -1) {
 458                         perror("LTT Error in sigsuspend\n");
 459                 }
 460                 if(traced_pid == 0) break; /* parent died */
 461                 if(parent_exited) break;
 462                 dbg_printf("LTT Doing a buffer switch read. pid is : %lu\n", getpid());
 463
 464                 do {
 465                         ret = read_subbuffer(&shared_trace_info->channel.process, fd_process);
 466                 } while(ret == 0);
 467         }
 468         /* The parent thread is dead and we have finished with the buffer */
 469
 470         /* Buffer force switch (flush). Using FLUSH instead of ACTIVE because we know
 471          * there is no writer. */
 472         flush_buffer(&shared_trace_info->channel.process, FORCE_FLUSH);
 473         do {
 474                 ret = read_subbuffer(&shared_trace_info->channel.process, fd_process);
 475         } while(ret == 0);
 476
 477         if(fd_process != -1)
 478                 close(fd_process);
 479
 480         ret = sem_destroy(&shared_trace_info->channel.process.writer_sem);
 481         if(ret < 0) {
 482                 perror("error in sem_destroy");
 483         }
 484         munmap(shared_trace_info, sizeof(*shared_trace_info));
 485
 486         exit(0);
 487 }
 488
 489
 490 /* Reader-writer initialization */
 491
 492 static enum ltt_process_role { LTT_ROLE_WRITER, LTT_ROLE_READER }
 493         role = LTT_ROLE_WRITER;
 494
 495
 496 void ltt_rw_init(void)
 497 {
 498         pid_t pid;
 499         struct ltt_trace_info *shared_trace_info;
 500         int ret;
 501         sigset_t set, oldset;
 502         pid_t l_traced_pid = getpid();
 503         pid_t l_traced_tid = gettid();
 504
 505         /* parent : create the shared memory map */
 506         shared_trace_info = mmap(0, sizeof(*thread_trace_info),
 507                         PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, 0, 0);
 508         shared_trace_info->init=0;
 509         shared_trace_info->filter=0;
 510         shared_trace_info->daemon_id=0;
 511         shared_trace_info->nesting=0;
 512         memset(&shared_trace_info->channel.process, 0,
 513                         sizeof(shared_trace_info->channel.process));
 514         //Need NPTL!
 515         ret = sem_init(&shared_trace_info->channel.process.writer_sem, 1,
 516                                                                         LTT_N_SUBBUFS);
 517         if(ret < 0) {
 518                 perror("error in sem_init");
 519         }
 520         shared_trace_info->channel.process.alloc_size = LTT_BUF_SIZE_PROCESS;
 521         shared_trace_info->channel.process.subbuf_size = LTT_SUBBUF_SIZE_PROCESS;
 522         shared_trace_info->channel.process.start =
 523                                                 shared_trace_info->channel.process_buf;
 524         ltt_buffer_begin_callback(&shared_trace_info->channel.process,
 525                         ltt_get_timestamp(), 0);
 526
 527         shared_trace_info->init = 1;
 528
 529         /* Disable signals */
 530   ret = sigfillset(&set);
 531   if(ret) {
 532     dbg_printf("LTT Error in sigfillset\n");
 533   }
 534
 535   ret = pthread_sigmask(SIG_BLOCK, &set, &oldset);
 536   if(ret) {
 537     dbg_printf("LTT Error in pthread_sigmask\n");
 538   }
 539
 540         pid = fork();
 541         if(pid > 0) {
 542                 /* Parent */
 543                 shared_trace_info->daemon_id = pid;
 544                 thread_trace_info = shared_trace_info;
 545
 546                 /* Enable signals */
 547                 ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 548                 if(ret) {
 549                         dbg_printf("LTT Error in pthread_sigmask\n");
 550                 }
 551         } else if(pid == 0) {
 552                 pid_t sid;
 553                 /* Child */
 554                 role = LTT_ROLE_READER;
 555                 sid = setsid();
 556                 //Not a good idea to renice, unless futex wait eventually implement
 557                 //priority inheritence.
 558                 //ret = nice(1);
 559                 //if(ret < 0) {
 560                 //      perror("Error in nice");
 561                 //}
 562                 if(sid < 0) {
 563                         perror("Error setting sid");
 564                 }
 565                 ltt_usertrace_fast_daemon(shared_trace_info, oldset, l_traced_pid,
 566                                         l_traced_tid);
 567                 /* Should never return */
 568                 exit(-1);
 569         } else if(pid < 0) {
 570                 /* fork error */
 571                 perror("LTT Error in forking ltt-usertrace-fast");
 572         }
 573 }
 574
 575 static __thread struct _pthread_cleanup_buffer cleanup_buffer;
 576
 577 void ltt_thread_init(void)
 578 {
 579         _pthread_cleanup_push(&cleanup_buffer, ltt_usertrace_fast_cleanup, NULL);
 580         ltt_rw_init();
 581 }
 582
 583 void __attribute__((constructor)) __ltt_usertrace_fast_init(void)
 584 {
 585   dbg_printf("LTT usertrace-fast init\n");
 586
 587         ltt_rw_init();
 588 }
 589
 590 void __attribute__((destructor)) __ltt_usertrace_fast_fini(void)
 591 {
 592         if(role == LTT_ROLE_WRITER) {
 593           dbg_printf("LTT usertrace-fast fini\n");
 594                 ltt_usertrace_fast_cleanup(NULL);
 595         }
 596 }
 597