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 "shash.h"
  29 #include "sset.h"
  30 #include "signals.h"
  31 #include "socket-util.h"
  32 #include "util.h"
  33 #include "vlog.h"
  34
  35 #include "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 HANDLE wevent;
  63 static volatile sig_atomic_t stored_sig_nr = SIG_ATOMIC_MAX;
  64
  65 static struct ovs_mutex mutex;
  66
  67 static void atexit_handler(void);
  68 static void call_hooks(int sig_nr);
  69 #ifdef _WIN32
  70 static BOOL WINAPI ConsoleHandlerRoutine(DWORD dwCtrlType);
  71 #endif
  72
  73 /* Initializes the fatal signal handling module.  Calling this function is
  74  * optional, because calling any other function in the module will also
  75  * initialize it.  However, in a multithreaded program, the module must be
  76  * initialized while the process is still single-threaded. */
  77 void
  78 fatal_signal_init(void)
  79 {
  80     static bool inited = false;
  81
  82     if (!inited) {
  83         size_t i;
  84
  85         assert_single_threaded();
  86         inited = true;
  87
  88         ovs_mutex_init_recursive(&mutex);
  89 #ifndef _WIN32
  90         xpipe_nonblocking(signal_fds);
  91 #else
  92         wevent = CreateEvent(NULL, TRUE, FALSE, NULL);
  93         if (!wevent) {
  94             char *msg_buf = ovs_lasterror_to_string();
  95             VLOG_FATAL("Failed to create a event (%s).", msg_buf);
  96         }
  97
  98         /* Register a function to handle Ctrl+C. */
  99         SetConsoleCtrlHandler(ConsoleHandlerRoutine, true);
 100 #endif
 101
 102         for (i = 0; i < ARRAY_SIZE(fatal_signals); i++) {
 103             int sig_nr = fatal_signals[i];
 104 #ifndef _WIN32
 105             struct sigaction old_sa;
 106
 107             xsigaction(sig_nr, NULL, &old_sa);
 108             if (old_sa.sa_handler == SIG_DFL
 109                 && signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
 110                 VLOG_FATAL("signal failed (%s)", ovs_strerror(errno));
 111             }
 112 #else
 113             if (signal(sig_nr, fatal_signal_handler) == SIG_ERR) {
 114                 VLOG_FATAL("signal failed (%s)", ovs_strerror(errno));
 115             }
 116 #endif
 117         }
 118         atexit(atexit_handler);
 119     }
 120 }
 121
 122 /* Registers 'hook_cb' to be called from inside poll_block() following a fatal
 123  * signal.  'hook_cb' does not need to be async-signal-safe.  In a
 124  * multithreaded program 'hook_cb' might be called from any thread, with
 125  * threads other than the one running 'hook_cb' in unknown states.
 126  *
 127  * If 'run_at_exit' is true, 'hook_cb' is also called during normal process
 128  * termination, e.g. when exit() is called or when main() returns.
 129  *
 130  * If the current process forks, fatal_signal_fork() may be called to clear the
 131  * parent process's fatal signal hooks, so that 'hook_cb' is only called when
 132  * the child terminates, not when the parent does.  When fatal_signal_fork() is
 133  * called, it calls the 'cancel_cb' function if it is nonnull, passing 'aux',
 134  * to notify that the hook has been canceled.  This allows the hook to free
 135  * memory, etc. */
 136 void
 137 fatal_signal_add_hook(void (*hook_cb)(void *aux), void (*cancel_cb)(void *aux),
 138                       void *aux, bool run_at_exit)
 139 {
 140     fatal_signal_init();
 141
 142     ovs_mutex_lock(&mutex);
 143     ovs_assert(n_hooks < MAX_HOOKS);
 144     hooks[n_hooks].hook_cb = hook_cb;
 145     hooks[n_hooks].cancel_cb = cancel_cb;
 146     hooks[n_hooks].aux = aux;
 147     hooks[n_hooks].run_at_exit = run_at_exit;
 148     n_hooks++;
 149     ovs_mutex_unlock(&mutex);
 150 }
 151
 152 /* Handles fatal signal number 'sig_nr'.
 153  *
 154  * Ordinarily this is the actual signal handler.  When other code needs to
 155  * handle one of our signals, however, it can register for that signal and, if
 156  * and when necessary, call this function to do fatal signal processing for it
 157  * and terminate the process.  Currently only timeval.c does this, for SIGALRM.
 158  * (It is not important whether the other code sets up its signal handler
 159  * before or after this file, because this file will only set up a signal
 160  * handler in the case where the signal has its default handling.)  */
 161 void
 162 fatal_signal_handler(int sig_nr)
 163 {
 164 #ifndef _WIN32
 165     ignore(write(signal_fds[1], "", 1));
 166 #else
 167     SetEvent(wevent);
 168 #endif
 169     stored_sig_nr = sig_nr;
 170 }
 171
 172 /* Check whether a fatal signal has occurred and, if so, call the fatal signal
 173  * hooks and exit.
 174  *
 175  * This function is called automatically by poll_block(), but specialized
 176  * programs that may not always call poll_block() on a regular basis should
 177  * also call it periodically.  (Therefore, any function with "block" in its
 178  * name should call fatal_signal_run() each time it is called, either directly
 179  * or through poll_block(), because such functions can only used by specialized
 180  * programs that can afford to block outside their main loop around
 181  * poll_block().)
 182  */
 183 void
 184 fatal_signal_run(void)
 185 {
 186     sig_atomic_t sig_nr;
 187
 188     fatal_signal_init();
 189
 190     sig_nr = stored_sig_nr;
 191     if (sig_nr != SIG_ATOMIC_MAX) {
 192         char namebuf[SIGNAL_NAME_BUFSIZE];
 193
 194         ovs_mutex_lock(&mutex);
 195
 196 #ifndef _WIN32
 197         VLOG_WARN("terminating with signal %d (%s)",
 198                   (int)sig_nr, signal_name(sig_nr, namebuf, sizeof namebuf));
 199 #else
 200         VLOG_WARN("terminating with signal %d", (int)sig_nr);
 201 #endif
 202         call_hooks(sig_nr);
 203
 204         /* Re-raise the signal with the default handling so that the program
 205          * termination status reflects that we were killed by this signal */
 206         signal(sig_nr, SIG_DFL);
 207         raise(sig_nr);
 208
 209         ovs_mutex_unlock(&mutex);
 210         OVS_NOT_REACHED();
 211     }
 212 }
 213
 214 void
 215 fatal_signal_wait(void)
 216 {
 217     fatal_signal_init();
 218     poll_fd_wait_event(signal_fds[0], wevent, POLLIN);
 219 }
 220
 221 void
 222 fatal_ignore_sigpipe(void)
 223 {
 224 #ifndef _WIN32
 225     signal(SIGPIPE, SIG_IGN);
 226 #endif
 227 }
 228
 229 static void
 230 atexit_handler(void)
 231 {
 232     call_hooks(0);
 233 }
 234
 235 static void
 236 call_hooks(int sig_nr)
 237 {
 238     static volatile sig_atomic_t recurse = 0;
 239     if (!recurse) {
 240         size_t i;
 241
 242         recurse = 1;
 243
 244         for (i = 0; i < n_hooks; i++) {
 245             struct hook *h = &hooks[i];
 246             if (sig_nr || h->run_at_exit) {
 247                 h->hook_cb(h->aux);
 248             }
 249         }
 250     }
 251 }
 252
 253 #ifdef _WIN32
 254 BOOL WINAPI ConsoleHandlerRoutine(DWORD dwCtrlType)
 255 {
 256     stored_sig_nr = SIGINT;
 257     SetEvent(wevent);
 258     return true;
 259 }
 260 #endif
 261 \f
 262 /* Files to delete on exit. */
 263 static struct sset files = SSET_INITIALIZER(&files);
 264
 265 /* Has a hook function been registered with fatal_signal_add_hook() (and not
 266  * cleared by fatal_signal_fork())? */
 267 static bool added_hook;
 268
 269 static void unlink_files(void *aux);
 270 static void cancel_files(void *aux);
 271 static void do_unlink_files(void);
 272
 273 /* Registers 'file' to be unlinked when the program terminates via exit() or a
 274  * fatal signal. */
 275 void
 276 fatal_signal_add_file_to_unlink(const char *file)
 277 {
 278     fatal_signal_init();
 279
 280     ovs_mutex_lock(&mutex);
 281     if (!added_hook) {
 282         added_hook = true;
 283         fatal_signal_add_hook(unlink_files, cancel_files, NULL, true);
 284     }
 285
 286     sset_add(&files, file);
 287     ovs_mutex_unlock(&mutex);
 288 }
 289
 290 /* Unregisters 'file' from being unlinked when the program terminates via
 291  * exit() or a fatal signal. */
 292 void
 293 fatal_signal_remove_file_to_unlink(const char *file)
 294 {
 295     fatal_signal_init();
 296
 297     ovs_mutex_lock(&mutex);
 298     sset_find_and_delete(&files, file);
 299     ovs_mutex_unlock(&mutex);
 300 }
 301
 302 /* Like fatal_signal_remove_file_to_unlink(), but also unlinks 'file'.
 303  * Returns 0 if successful, otherwise a positive errno value. */
 304 int
 305 fatal_signal_unlink_file_now(const char *file)
 306 {
 307     int error;
 308
 309     fatal_signal_init();
 310
 311     ovs_mutex_lock(&mutex);
 312
 313     error = unlink(file) ? errno : 0;
 314     if (error) {
 315         VLOG_WARN("could not unlink \"%s\" (%s)", file, ovs_strerror(error));
 316     }
 317
 318     fatal_signal_remove_file_to_unlink(file);
 319
 320     ovs_mutex_unlock(&mutex);
 321
 322     return error;
 323 }
 324
 325 static void
 326 unlink_files(void *aux OVS_UNUSED)
 327 {
 328     do_unlink_files();
 329 }
 330
 331 static void
 332 cancel_files(void *aux OVS_UNUSED)
 333 {
 334     sset_clear(&files);
 335     added_hook = false;
 336 }
 337
 338 static void
 339 do_unlink_files(void)
 340 {
 341     const char *file;
 342
 343     SSET_FOR_EACH (file, &files) {
 344         unlink(file);
 345     }
 346 }
 347 \f
 348 /* Clears all of the fatal signal hooks without executing them.  If any of the
 349  * hooks passed a 'cancel_cb' function to fatal_signal_add_hook(), then those
 350  * functions will be called, allowing them to free resources, etc.
 351  *
 352  * Following a fork, one of the resulting processes can call this function to
 353  * allow it to terminate without calling the hooks registered before calling
 354  * this function.  New hooks registered after calling this function will take
 355  * effect normally. */
 356 void
 357 fatal_signal_fork(void)
 358 {
 359     size_t i;
 360
 361     assert_single_threaded();
 362
 363     for (i = 0; i < n_hooks; i++) {
 364         struct hook *h = &hooks[i];
 365         if (h->cancel_cb) {
 366             h->cancel_cb(h->aux);
 367         }
 368     }
 369     n_hooks = 0;
 370
 371     /* Raise any signals that we have already received with the default
 372      * handler. */
 373     if (stored_sig_nr != SIG_ATOMIC_MAX) {
 374         raise(stored_sig_nr);
 375     }
 376 }