lib/fatal-signal.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16 #include <config.h>
  17 #include "fatal-signal.h"
  18 #include <errno.h>
  19 #include <signal.h>
  20 #include <stdbool.h>
  21 #include <stdio.h>
  22 #include <stdint.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include "ovs-thread.h"
  27 #include "poll-loop.h"
  28 #include "openvswitch/shash.h"
  29 #include "sset.h"
  30 #include "signals.h"
  31 #include "socket-util.h"
  32 #include "util.h"
  33 #include "openvswitch/vlog.h"
  34
  35 #include "openvswitch/type-props.h"
  36
  37 #ifndef SIG_ATOMIC_MAX
  38 #define SIG_ATOMIC_MAX TYPE_MAXIMUM(sig_atomic_t)
  39 #endif
  40
  41 VLOG_DEFINE_THIS_MODULE(fatal_signal);
  42
  43 /* Signals to catch. */
  44 #ifndef _WIN32
  45 static const int fatal_signals[] = { SIGTERM, SIGINT, SIGHUP, SIGALRM };
  46 #else
  47 static const int fatal_signals[] = { SIGTERM };
  48 #endif
  49
  50 /* Hooks to call upon catching a signal */
  51 struct hook {
  52     void (*hook_cb)(void *aux);
  53     void (*cancel_cb)(void *aux);
  54     void *aux;
  55     bool run_at_exit;
  56 };
  57 #define MAX_HOOKS 32
  58 static struct hook hooks[MAX_HOOKS];
  59 static size_t n_hooks;
  60
  61 static int signal_fds[2];
  62 static volatile sig_atomic_t stored_sig_nr = SIG_ATOMIC_MAX;
  63
  64 #ifdef _WIN32
  65 static HANDLE wevent;
  66 #endif
  67
  68 static struct ovs_mutex mutex;
  69
  70 static void call_hooks(int sig_nr);
  71 #ifdef _WIN32
  72 static BOOL WINAPI ConsoleHandlerRoutine(DWORD dwCtrlType);
  73 #endif
  74
  75 /* Initializes the fatal signal handling module.  Calling this function is
  76  * optional, because calling any other function in the module will also
  77  * initialize it.  However, in a multithreaded program, the module must be
  78  * initialized while the process is still single-threaded. */
  79 void
  80 fatal_signal_init(void)
  81 {
  82     static bool inited = false;
  83
  84     if (!inited) {
  85         size_t i;
  86
  87         assert_single_threaded();
  88         inited = true;
  89
  90         ovs_mutex_init_recursive(&mutex);
  91 #ifndef _WIN32
  92         xpipe_nonblocking(signal_fds);
  93 #else
  94         wevent = CreateEvent(NULL, TRUE, FALSE, NULL);
  95         if (!wevent) {
  96             char *msg_buf = ovs_lasterror_to_string();
  97             VLOG_FATAL("Failed to create a event (%s).", msg_buf);
  98         }
  99
 100         /* Register a function to handle Ctrl+C. */
 101         SetConsoleCtrlHandler(ConsoleHandlerRoutine, true);
 102 #endif
 103
 104         for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
 105             int sig_nr = fatal_signals[i];
 106 #ifndef _WIN32
 107             struct sigaction old_sa;
 108
 109             xsigaction(sig_nr, NULL, &old_sa);
 110             if (old_sa.sa_handler == SIG_DFL
 111                 && signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
 112                 VLOG_FATAL("signal failed (%s)", ovs_strerror(errno));
 113             }
 114 #else
 115             if (signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
 116                 VLOG_FATAL("signal failed (%s)", ovs_strerror(errno));
 117             }
 118 #endif
 119         }
 120         atexit(fatal_signal_atexit_handler);
 121     }
 122 }
 123
 124 /* Registers 'hook_cb' to be called from inside poll_block() following a fatal
 125  * signal.  'hook_cb' does not need to be async-signal-safe.  In a
 126  * multithreaded program 'hook_cb' might be called from any thread, with
 127  * threads other than the one running 'hook_cb' in unknown states.
 128  *
 129  * If 'run_at_exit' is true, 'hook_cb' is also called during normal process
 130  * termination, e.g. when exit() is called or when main() returns.
 131  *
 132  * If the current process forks, fatal_signal_fork() may be called to clear the
 133  * parent process's fatal signal hooks, so that 'hook_cb' is only called when
 134  * the child terminates, not when the parent does.  When fatal_signal_fork() is
 135  * called, it calls the 'cancel_cb' function if it is nonnull, passing 'aux',
 136  * to notify that the hook has been canceled.  This allows the hook to free
 137  * memory, etc. */
 138 void
 139 fatal_signal_add_hook(void (*hook_cb)(void *aux), void (*cancel_cb)(void *aux),
 140                       void *aux, bool run_at_exit)
 141 {
 142     fatal_signal_init();
 143
 144     ovs_mutex_lock(&mutex);
 145     ovs_assert(n_hooks < MAX_HOOKS);
 146     hooks[n_hooks].hook_cb = hook_cb;
 147     hooks[n_hooks].cancel_cb = cancel_cb;
 148     hooks[n_hooks].aux = aux;
 149     hooks[n_hooks].run_at_exit = run_at_exit;
 150     n_hooks++;
 151     ovs_mutex_unlock(&mutex);
 152 }
 153
 154 /* Handles fatal signal number 'sig_nr'.
 155  *
 156  * Ordinarily this is the actual signal handler.  When other code needs to
 157  * handle one of our signals, however, it can register for that signal and, if
 158  * and when necessary, call this function to do fatal signal processing for it
 159  * and terminate the process.  Currently only timeval.c does this, for SIGALRM.
 160  * (It is not important whether the other code sets up its signal handler
 161  * before or after this file, because this file will only set up a signal
 162  * handler in the case where the signal has its default handling.)  */
 163 void
 164 fatal_signal_handler(int sig_nr)
 165 {
 166 #ifndef _WIN32
 167     ignore(write(signal_fds[1], "", 1));
 168 #else
 169     SetEvent(wevent);
 170 #endif
 171     stored_sig_nr = sig_nr;
 172 }
 173
 174 /* Check whether a fatal signal has occurred and, if so, call the fatal signal
 175  * hooks and exit.
 176  *
 177  * This function is called automatically by poll_block(), but specialized
 178  * programs that may not always call poll_block() on a regular basis should
 179  * also call it periodically.  (Therefore, any function with "block" in its
 180  * name should call fatal_signal_run() each time it is called, either directly
 181  * or through poll_block(), because such functions can only used by specialized
 182  * programs that can afford to block outside their main loop around
 183  * poll_block().)
 184  */
 185 void
 186 fatal_signal_run(void)
 187 {
 188     sig_atomic_t sig_nr;
 189
 190     fatal_signal_init();
 191
 192     sig_nr = stored_sig_nr;
 193     if (sig_nr != SIG_ATOMIC_MAX) {
 194         char namebuf[SIGNAL_NAME_BUFSIZE];
 195
 196         ovs_mutex_lock(&mutex);
 197
 198 #ifndef _WIN32
 199         VLOG_WARN("terminating with signal %d (%s)",
 200                   (int)sig_nr, signal_name(sig_nr, namebuf, sizeof namebuf));
 201 #else
 202         VLOG_WARN("terminating with signal %d", (int)sig_nr);
 203 #endif
 204         call_hooks(sig_nr);
 205         fflush(stderr);
 206
 207         /* Re-raise the signal with the default handling so that the program
 208          * termination status reflects that we were killed by this signal */
 209         signal(sig_nr, SIG_DFL);
 210         raise(sig_nr);
 211
 212         ovs_mutex_unlock(&mutex);
 213         OVS_NOT_REACHED();
 214     }
 215 }
 216
 217 void
 218 fatal_signal_wait(void)
 219 {
 220     fatal_signal_init();
 221 #ifdef _WIN32
 222     poll_wevent_wait(wevent);
 223 #else
 224     poll_fd_wait(signal_fds[0], POLLIN);
 225 #endif
 226 }
 227
 228 void
 229 fatal_ignore_sigpipe(void)
 230 {
 231 #ifndef _WIN32
 232     signal(SIGPIPE, SIG_IGN);
 233 #endif
 234 }
 235
 236 void
 237 fatal_signal_atexit_handler(void)
 238 {
 239     call_hooks(0);
 240 }
 241
 242 static void
 243 call_hooks(int sig_nr)
 244 {
 245     static volatile sig_atomic_t recurse = 0;
 246     if (!recurse) {
 247         size_t i;
 248
 249         recurse = 1;
 250
 251         for (i = 0; i < n_hooks; i++) {
 252             struct hook *h = &hooks[i];
 253             if (sig_nr || h->run_at_exit) {
 254                 h->hook_cb(h->aux);
 255             }
 256         }
 257     }
 258 }
 259
 260 #ifdef _WIN32
 261 BOOL WINAPI ConsoleHandlerRoutine(DWORD dwCtrlType)
 262 {
 263     stored_sig_nr = SIGINT;
 264     SetEvent(wevent);
 265     return true;
 266 }
 267 #endif
 268 \f
 269 /* Files to delete on exit. */
 270 static struct sset files = SSET_INITIALIZER(&files);
 271
 272 /* Has a hook function been registered with fatal_signal_add_hook() (and not
 273  * cleared by fatal_signal_fork())? */
 274 static bool added_hook;
 275
 276 static void unlink_files(void *aux);
 277 static void cancel_files(void *aux);
 278 static void do_unlink_files(void);
 279
 280 /* Registers 'file' to be unlinked when the program terminates via exit() or a
 281  * fatal signal. */
 282 void
 283 fatal_signal_add_file_to_unlink(const char *file)
 284 {
 285     fatal_signal_init();
 286
 287     ovs_mutex_lock(&mutex);
 288     if (!added_hook) {
 289         added_hook = true;
 290         fatal_signal_add_hook(unlink_files, cancel_files, NULL, true);
 291     }
 292
 293     sset_add(&files, file);
 294     ovs_mutex_unlock(&mutex);
 295 }
 296
 297 /* Unregisters 'file' from being unlinked when the program terminates via
 298  * exit() or a fatal signal. */
 299 void
 300 fatal_signal_remove_file_to_unlink(const char *file)
 301 {
 302     fatal_signal_init();
 303
 304     ovs_mutex_lock(&mutex);
 305     sset_find_and_delete(&files, file);
 306     ovs_mutex_unlock(&mutex);
 307 }
 308
 309 /* Like fatal_signal_remove_file_to_unlink(), but also unlinks 'file'.
 310  * Returns 0 if successful, otherwise a positive errno value. */
 311 int
 312 fatal_signal_unlink_file_now(const char *file)
 313 {
 314     int error;
 315
 316     fatal_signal_init();
 317
 318     ovs_mutex_lock(&mutex);
 319
 320     error = unlink(file) ? errno : 0;
 321     if (error) {
 322         VLOG_WARN("could not unlink \"%s\" (%s)", file, ovs_strerror(error));
 323     }
 324
 325     fatal_signal_remove_file_to_unlink(file);
 326
 327     ovs_mutex_unlock(&mutex);
 328
 329     return error;
 330 }
 331
 332 static void
 333 unlink_files(void *aux OVS_UNUSED)
 334 {
 335     do_unlink_files();
 336 }
 337
 338 static void
 339 cancel_files(void *aux OVS_UNUSED)
 340 {
 341     sset_clear(&files);
 342     added_hook = false;
 343 }
 344
 345 static void
 346 do_unlink_files(void)
 347 {
 348     const char *file;
 349
 350     SSET_FOR_EACH (file, &files) {
 351         unlink(file);
 352     }
 353 }
 354 \f
 355 /* Clears all of the fatal signal hooks without executing them.  If any of the
 356  * hooks passed a 'cancel_cb' function to fatal_signal_add_hook(), then those
 357  * functions will be called, allowing them to free resources, etc.
 358  *
 359  * Following a fork, one of the resulting processes can call this function to
 360  * allow it to terminate without calling the hooks registered before calling
 361  * this function.  New hooks registered after calling this function will take
 362  * effect normally. */
 363 void
 364 fatal_signal_fork(void)
 365 {
 366     size_t i;
 367
 368     assert_single_threaded();
 369
 370     for (i = 0; i < n_hooks; i++) {
 371         struct hook *h = &hooks[i];
 372         if (h->cancel_cb) {
 373             h->cancel_cb(h->aux);
 374         }
 375     }
 376     n_hooks = 0;
 377
 378     /* Raise any signals that we have already received with the default
 379      * handler. */
 380     if (stored_sig_nr != SIG_ATOMIC_MAX) {
 381         raise(stored_sig_nr);
 382     }
 383 }
 384
 385 #ifndef _WIN32
 386 /* Blocks all fatal signals and returns previous signal mask into
 387  * 'prev_mask'. */
 388 void
 389 fatal_signal_block(sigset_t *prev_mask)
 390 {
 391     int i;
 392     sigset_t block_mask;
 393
 394     sigemptyset(&block_mask);
 395     for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
 396         int sig_nr = fatal_signals[i];
 397         sigaddset(&block_mask, sig_nr);
 398     }
 399     xpthread_sigmask(SIG_BLOCK, &block_mask, prev_mask);
 400 }
 401 #endif