fs/timerfd.c

   1 /*
   2  *  fs/timerfd.c
   3  *
   4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   5  *
   6  *
   7  *  Thanks to Thomas Gleixner for code reviews and useful comments.
   8  *
   9  */
  10
  11 #include <linux/alarmtimer.h>
  12 #include <linux/file.h>
  13 #include <linux/poll.h>
  14 #include <linux/init.h>
  15 #include <linux/fs.h>
  16 #include <linux/sched.h>
  17 #include <linux/kernel.h>
  18 #include <linux/slab.h>
  19 #include <linux/list.h>
  20 #include <linux/spinlock.h>
  21 #include <linux/time.h>
  22 #include <linux/hrtimer.h>
  23 #include <linux/anon_inodes.h>
  24 #include <linux/timerfd.h>
  25 #include <linux/syscalls.h>
  26 #include <linux/compat.h>
  27 #include <linux/rcupdate.h>
  28
  29 struct timerfd_ctx {
  30         union {
  31                 struct hrtimer tmr;
  32                 struct alarm alarm;
  33         } t;
  34         ktime_t tintv;
  35         ktime_t moffs;
  36         wait_queue_head_t wqh;
  37         u64 ticks;
  38         int clockid;
  39         short unsigned expired;
  40         short unsigned settime_flags;   /* to show in fdinfo */
  41         struct rcu_head rcu;
  42         struct list_head clist;
  43         bool might_cancel;
  44 };
  45
  46 static LIST_HEAD(cancel_list);
  47 static DEFINE_SPINLOCK(cancel_lock);
  48
  49 static inline bool isalarm(struct timerfd_ctx *ctx)
  50 {
  51         return ctx->clockid == CLOCK_REALTIME_ALARM ||
  52                 ctx->clockid == CLOCK_BOOTTIME_ALARM;
  53 }
  54
  55 /*
  56  * This gets called when the timer event triggers. We set the "expired"
  57  * flag, but we do not re-arm the timer (in case it's necessary,
  58  * tintv.tv64 != 0) until the timer is accessed.
  59  */
  60 static void timerfd_triggered(struct timerfd_ctx *ctx)
  61 {
  62         unsigned long flags;
  63
  64         spin_lock_irqsave(&ctx->wqh.lock, flags);
  65         ctx->expired = 1;
  66         ctx->ticks++;
  67         wake_up_locked(&ctx->wqh);
  68         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  69 }
  70
  71 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
  72 {
  73         struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
  74                                                t.tmr);
  75         timerfd_triggered(ctx);
  76         return HRTIMER_NORESTART;
  77 }
  78
  79 static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
  80         ktime_t now)
  81 {
  82         struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
  83                                                t.alarm);
  84         timerfd_triggered(ctx);
  85         return ALARMTIMER_NORESTART;
  86 }
  87
  88 /*
  89  * Called when the clock was set to cancel the timers in the cancel
  90  * list. This will wake up processes waiting on these timers. The
  91  * wake-up requires ctx->ticks to be non zero, therefore we increment
  92  * it before calling wake_up_locked().
  93  */
  94 void timerfd_clock_was_set(void)
  95 {
  96         ktime_t moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
  97         struct timerfd_ctx *ctx;
  98         unsigned long flags;
  99
 100         rcu_read_lock();
 101         list_for_each_entry_rcu(ctx, &cancel_list, clist) {
 102                 if (!ctx->might_cancel)
 103                         continue;
 104                 spin_lock_irqsave(&ctx->wqh.lock, flags);
 105                 if (ctx->moffs.tv64 != moffs.tv64) {
 106                         ctx->moffs.tv64 = KTIME_MAX;
 107                         ctx->ticks++;
 108                         wake_up_locked(&ctx->wqh);
 109                 }
 110                 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 111         }
 112         rcu_read_unlock();
 113 }
 114
 115 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
 116 {
 117         if (ctx->might_cancel) {
 118                 ctx->might_cancel = false;
 119                 spin_lock(&cancel_lock);
 120                 list_del_rcu(&ctx->clist);
 121                 spin_unlock(&cancel_lock);
 122         }
 123 }
 124
 125 static bool timerfd_canceled(struct timerfd_ctx *ctx)
 126 {
 127         if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
 128                 return false;
 129         ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
 130         return true;
 131 }
 132
 133 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
 134 {
 135         if ((ctx->clockid == CLOCK_REALTIME ||
 136              ctx->clockid == CLOCK_REALTIME_ALARM) &&
 137             (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
 138                 if (!ctx->might_cancel) {
 139                         ctx->might_cancel = true;
 140                         spin_lock(&cancel_lock);
 141                         list_add_rcu(&ctx->clist, &cancel_list);
 142                         spin_unlock(&cancel_lock);
 143                 }
 144         } else if (ctx->might_cancel) {
 145                 timerfd_remove_cancel(ctx);
 146         }
 147 }
 148
 149 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
 150 {
 151         ktime_t remaining;
 152
 153         if (isalarm(ctx))
 154                 remaining = alarm_expires_remaining(&ctx->t.alarm);
 155         else
 156                 remaining = hrtimer_expires_remaining(&ctx->t.tmr);
 157
 158         return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
 159 }
 160
 161 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
 162                          const struct itimerspec *ktmr)
 163 {
 164         enum hrtimer_mode htmode;
 165         ktime_t texp;
 166         int clockid = ctx->clockid;
 167
 168         htmode = (flags & TFD_TIMER_ABSTIME) ?
 169                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
 170
 171         texp = timespec_to_ktime(ktmr->it_value);
 172         ctx->expired = 0;
 173         ctx->ticks = 0;
 174         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
 175
 176         if (isalarm(ctx)) {
 177                 alarm_init(&ctx->t.alarm,
 178                            ctx->clockid == CLOCK_REALTIME_ALARM ?
 179                            ALARM_REALTIME : ALARM_BOOTTIME,
 180                            timerfd_alarmproc);
 181         } else {
 182                 hrtimer_init(&ctx->t.tmr, clockid, htmode);
 183                 hrtimer_set_expires(&ctx->t.tmr, texp);
 184                 ctx->t.tmr.function = timerfd_tmrproc;
 185         }
 186
 187         if (texp.tv64 != 0) {
 188                 if (isalarm(ctx)) {
 189                         if (flags & TFD_TIMER_ABSTIME)
 190                                 alarm_start(&ctx->t.alarm, texp);
 191                         else
 192                                 alarm_start_relative(&ctx->t.alarm, texp);
 193                 } else {
 194                         hrtimer_start(&ctx->t.tmr, texp, htmode);
 195                 }
 196
 197                 if (timerfd_canceled(ctx))
 198                         return -ECANCELED;
 199         }
 200
 201         ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
 202         return 0;
 203 }
 204
 205 static int timerfd_release(struct inode *inode, struct file *file)
 206 {
 207         struct timerfd_ctx *ctx = file->private_data;
 208
 209         timerfd_remove_cancel(ctx);
 210
 211         if (isalarm(ctx))
 212                 alarm_cancel(&ctx->t.alarm);
 213         else
 214                 hrtimer_cancel(&ctx->t.tmr);
 215         kfree_rcu(ctx, rcu);
 216         return 0;
 217 }
 218
 219 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
 220 {
 221         struct timerfd_ctx *ctx = file->private_data;
 222         unsigned int events = 0;
 223         unsigned long flags;
 224
 225         poll_wait(file, &ctx->wqh, wait);
 226
 227         spin_lock_irqsave(&ctx->wqh.lock, flags);
 228         if (ctx->ticks)
 229                 events |= POLLIN;
 230         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 231
 232         return events;
 233 }
 234
 235 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
 236                             loff_t *ppos)
 237 {
 238         struct timerfd_ctx *ctx = file->private_data;
 239         ssize_t res;
 240         u64 ticks = 0;
 241
 242         if (count < sizeof(ticks))
 243                 return -EINVAL;
 244         spin_lock_irq(&ctx->wqh.lock);
 245         if (file->f_flags & O_NONBLOCK)
 246                 res = -EAGAIN;
 247         else
 248                 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
 249
 250         /*
 251          * If clock has changed, we do not care about the
 252          * ticks and we do not rearm the timer. Userspace must
 253          * reevaluate anyway.
 254          */
 255         if (timerfd_canceled(ctx)) {
 256                 ctx->ticks = 0;
 257                 ctx->expired = 0;
 258                 res = -ECANCELED;
 259         }
 260
 261         if (ctx->ticks) {
 262                 ticks = ctx->ticks;
 263
 264                 if (ctx->expired && ctx->tintv.tv64) {
 265                         /*
 266                          * If tintv.tv64 != 0, this is a periodic timer that
 267                          * needs to be re-armed. We avoid doing it in the timer
 268                          * callback to avoid DoS attacks specifying a very
 269                          * short timer period.
 270                          */
 271                         if (isalarm(ctx)) {
 272                                 ticks += alarm_forward_now(
 273                                         &ctx->t.alarm, ctx->tintv) - 1;
 274                                 alarm_restart(&ctx->t.alarm);
 275                         } else {
 276                                 ticks += hrtimer_forward_now(&ctx->t.tmr,
 277                                                              ctx->tintv) - 1;
 278                                 hrtimer_restart(&ctx->t.tmr);
 279                         }
 280                 }
 281                 ctx->expired = 0;
 282                 ctx->ticks = 0;
 283         }
 284         spin_unlock_irq(&ctx->wqh.lock);
 285         if (ticks)
 286                 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
 287         return res;
 288 }
 289
 290 #ifdef CONFIG_PROC_FS
 291 static int timerfd_show(struct seq_file *m, struct file *file)
 292 {
 293         struct timerfd_ctx *ctx = file->private_data;
 294         struct itimerspec t;
 295
 296         spin_lock_irq(&ctx->wqh.lock);
 297         t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 298         t.it_interval = ktime_to_timespec(ctx->tintv);
 299         spin_unlock_irq(&ctx->wqh.lock);
 300
 301         return seq_printf(m,
 302                           "clockid: %d\n"
 303                           "ticks: %llu\n"
 304                           "settime flags: 0%o\n"
 305                           "it_value: (%llu, %llu)\n"
 306                           "it_interval: (%llu, %llu)\n",
 307                           ctx->clockid, (unsigned long long)ctx->ticks,
 308                           ctx->settime_flags,
 309                           (unsigned long long)t.it_value.tv_sec,
 310                           (unsigned long long)t.it_value.tv_nsec,
 311                           (unsigned long long)t.it_interval.tv_sec,
 312                           (unsigned long long)t.it_interval.tv_nsec);
 313 }
 314 #else
 315 #define timerfd_show NULL
 316 #endif
 317
 318 #ifdef CONFIG_CHECKPOINT_RESTORE
 319 static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 320 {
 321         struct timerfd_ctx *ctx = file->private_data;
 322         int ret = 0;
 323
 324         switch (cmd) {
 325         case TFD_IOC_SET_TICKS: {
 326                 u64 ticks;
 327
 328                 if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
 329                         return -EFAULT;
 330                 if (!ticks)
 331                         return -EINVAL;
 332
 333                 spin_lock_irq(&ctx->wqh.lock);
 334                 if (!timerfd_canceled(ctx)) {
 335                         ctx->ticks = ticks;
 336                         wake_up_locked(&ctx->wqh);
 337                 } else
 338                         ret = -ECANCELED;
 339                 spin_unlock_irq(&ctx->wqh.lock);
 340                 break;
 341         }
 342         default:
 343                 ret = -ENOTTY;
 344                 break;
 345         }
 346
 347         return ret;
 348 }
 349 #else
 350 #define timerfd_ioctl NULL
 351 #endif
 352
 353 static const struct file_operations timerfd_fops = {
 354         .release        = timerfd_release,
 355         .poll           = timerfd_poll,
 356         .read           = timerfd_read,
 357         .llseek         = noop_llseek,
 358         .show_fdinfo    = timerfd_show,
 359         .unlocked_ioctl = timerfd_ioctl,
 360 };
 361
 362 static int timerfd_fget(int fd, struct fd *p)
 363 {
 364         struct fd f = fdget(fd);
 365         if (!f.file)
 366                 return -EBADF;
 367         if (f.file->f_op != &timerfd_fops) {
 368                 fdput(f);
 369                 return -EINVAL;
 370         }
 371         *p = f;
 372         return 0;
 373 }
 374
 375 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 376 {
 377         int ufd;
 378         struct timerfd_ctx *ctx;
 379
 380         /* Check the TFD_* constants for consistency.  */
 381         BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
 382         BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
 383
 384         if ((flags & ~TFD_CREATE_FLAGS) ||
 385             (clockid != CLOCK_MONOTONIC &&
 386              clockid != CLOCK_REALTIME &&
 387              clockid != CLOCK_REALTIME_ALARM &&
 388              clockid != CLOCK_BOOTTIME &&
 389              clockid != CLOCK_BOOTTIME_ALARM))
 390                 return -EINVAL;
 391
 392         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 393         if (!ctx)
 394                 return -ENOMEM;
 395
 396         init_waitqueue_head(&ctx->wqh);
 397         ctx->clockid = clockid;
 398
 399         if (isalarm(ctx))
 400                 alarm_init(&ctx->t.alarm,
 401                            ctx->clockid == CLOCK_REALTIME_ALARM ?
 402                            ALARM_REALTIME : ALARM_BOOTTIME,
 403                            timerfd_alarmproc);
 404         else
 405                 hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
 406
 407         ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
 408
 409         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
 410                                O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
 411         if (ufd < 0)
 412                 kfree(ctx);
 413
 414         return ufd;
 415 }
 416
 417 static int do_timerfd_settime(int ufd, int flags,
 418                 const struct itimerspec *new,
 419                 struct itimerspec *old)
 420 {
 421         struct fd f;
 422         struct timerfd_ctx *ctx;
 423         int ret;
 424
 425         if ((flags & ~TFD_SETTIME_FLAGS) ||
 426             !timespec_valid(&new->it_value) ||
 427             !timespec_valid(&new->it_interval))
 428                 return -EINVAL;
 429
 430         ret = timerfd_fget(ufd, &f);
 431         if (ret)
 432                 return ret;
 433         ctx = f.file->private_data;
 434
 435         timerfd_setup_cancel(ctx, flags);
 436
 437         /*
 438          * We need to stop the existing timer before reprogramming
 439          * it to the new values.
 440          */
 441         for (;;) {
 442                 spin_lock_irq(&ctx->wqh.lock);
 443
 444                 if (isalarm(ctx)) {
 445                         if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
 446                                 break;
 447                 } else {
 448                         if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
 449                                 break;
 450                 }
 451                 spin_unlock_irq(&ctx->wqh.lock);
 452                 cpu_relax();
 453         }
 454
 455         /*
 456          * If the timer is expired and it's periodic, we need to advance it
 457          * because the caller may want to know the previous expiration time.
 458          * We do not update "ticks" and "expired" since the timer will be
 459          * re-programmed again in the following timerfd_setup() call.
 460          */
 461         if (ctx->expired && ctx->tintv.tv64) {
 462                 if (isalarm(ctx))
 463                         alarm_forward_now(&ctx->t.alarm, ctx->tintv);
 464                 else
 465                         hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
 466         }
 467
 468         old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 469         old->it_interval = ktime_to_timespec(ctx->tintv);
 470
 471         /*
 472          * Re-program the timer to the new value ...
 473          */
 474         ret = timerfd_setup(ctx, flags, new);
 475
 476         spin_unlock_irq(&ctx->wqh.lock);
 477         fdput(f);
 478         return ret;
 479 }
 480
 481 static int do_timerfd_gettime(int ufd, struct itimerspec *t)
 482 {
 483         struct fd f;
 484         struct timerfd_ctx *ctx;
 485         int ret = timerfd_fget(ufd, &f);
 486         if (ret)
 487                 return ret;
 488         ctx = f.file->private_data;
 489
 490         spin_lock_irq(&ctx->wqh.lock);
 491         if (ctx->expired && ctx->tintv.tv64) {
 492                 ctx->expired = 0;
 493
 494                 if (isalarm(ctx)) {
 495                         ctx->ticks +=
 496                                 alarm_forward_now(
 497                                         &ctx->t.alarm, ctx->tintv) - 1;
 498                         alarm_restart(&ctx->t.alarm);
 499                 } else {
 500                         ctx->ticks +=
 501                                 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
 502                                 - 1;
 503                         hrtimer_restart(&ctx->t.tmr);
 504                 }
 505         }
 506         t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 507         t->it_interval = ktime_to_timespec(ctx->tintv);
 508         spin_unlock_irq(&ctx->wqh.lock);
 509         fdput(f);
 510         return 0;
 511 }
 512
 513 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 514                 const struct itimerspec __user *, utmr,
 515                 struct itimerspec __user *, otmr)
 516 {
 517         struct itimerspec new, old;
 518         int ret;
 519
 520         if (copy_from_user(&new, utmr, sizeof(new)))
 521                 return -EFAULT;
 522         ret = do_timerfd_settime(ufd, flags, &new, &old);
 523         if (ret)
 524                 return ret;
 525         if (otmr && copy_to_user(otmr, &old, sizeof(old)))
 526                 return -EFAULT;
 527
 528         return ret;
 529 }
 530
 531 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
 532 {
 533         struct itimerspec kotmr;
 534         int ret = do_timerfd_gettime(ufd, &kotmr);
 535         if (ret)
 536                 return ret;
 537         return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
 538 }
 539
 540 #ifdef CONFIG_COMPAT
 541 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 542                 const struct compat_itimerspec __user *, utmr,
 543                 struct compat_itimerspec __user *, otmr)
 544 {
 545         struct itimerspec new, old;
 546         int ret;
 547
 548         if (get_compat_itimerspec(&new, utmr))
 549                 return -EFAULT;
 550         ret = do_timerfd_settime(ufd, flags, &new, &old);
 551         if (ret)
 552                 return ret;
 553         if (otmr && put_compat_itimerspec(otmr, &old))
 554                 return -EFAULT;
 555         return ret;
 556 }
 557
 558 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
 559                 struct compat_itimerspec __user *, otmr)
 560 {
 561         struct itimerspec kotmr;
 562         int ret = do_timerfd_gettime(ufd, &kotmr);
 563         if (ret)
 564                 return ret;
 565         return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
 566 }
 567 #endif