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