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         spinlock_t cancel_lock;
  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_get_monotonic_offset();
  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 void timerfd_remove_cancel(struct timerfd_ctx *ctx)
 126 {
 127         spin_lock(&ctx->cancel_lock);
 128         __timerfd_remove_cancel(ctx);
 129         spin_unlock(&ctx->cancel_lock);
 130 }
 131
 132 static bool timerfd_canceled(struct timerfd_ctx *ctx)
 133 {
 134         if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
 135                 return false;
 136         ctx->moffs = ktime_get_monotonic_offset();
 137         return true;
 138 }
 139
 140 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
 141 {
 142         spin_lock(&ctx->cancel_lock);
 143         if ((ctx->clockid == CLOCK_REALTIME ||
 144              ctx->clockid == CLOCK_REALTIME_ALARM) &&
 145             (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
 146                 if (!ctx->might_cancel) {
 147                         ctx->might_cancel = true;
 148                         spin_lock(&cancel_lock);
 149                         list_add_rcu(&ctx->clist, &cancel_list);
 150                         spin_unlock(&cancel_lock);
 151                 }
 152         } else {
 153                 __timerfd_remove_cancel(ctx);
 154         }
 155         spin_unlock(&ctx->cancel_lock);
 156 }
 157
 158 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
 159 {
 160         ktime_t remaining;
 161
 162         if (isalarm(ctx))
 163                 remaining = alarm_expires_remaining(&ctx->t.alarm);
 164         else
 165                 remaining = hrtimer_expires_remaining(&ctx->t.tmr);
 166
 167         return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
 168 }
 169
 170 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
 171                          const struct itimerspec *ktmr)
 172 {
 173         enum hrtimer_mode htmode;
 174         ktime_t texp;
 175         int clockid = ctx->clockid;
 176
 177         htmode = (flags & TFD_TIMER_ABSTIME) ?
 178                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
 179
 180         texp = timespec_to_ktime(ktmr->it_value);
 181         ctx->expired = 0;
 182         ctx->ticks = 0;
 183         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
 184
 185         if (isalarm(ctx)) {
 186                 alarm_init(&ctx->t.alarm,
 187                            ctx->clockid == CLOCK_REALTIME_ALARM ?
 188                            ALARM_REALTIME : ALARM_BOOTTIME,
 189                            timerfd_alarmproc);
 190         } else {
 191                 hrtimer_init(&ctx->t.tmr, clockid, htmode);
 192                 hrtimer_set_expires(&ctx->t.tmr, texp);
 193                 ctx->t.tmr.function = timerfd_tmrproc;
 194         }
 195
 196         if (texp.tv64 != 0) {
 197                 if (isalarm(ctx)) {
 198                         if (flags & TFD_TIMER_ABSTIME)
 199                                 alarm_start(&ctx->t.alarm, texp);
 200                         else
 201                                 alarm_start_relative(&ctx->t.alarm, texp);
 202                 } else {
 203                         hrtimer_start(&ctx->t.tmr, texp, htmode);
 204                 }
 205
 206                 if (timerfd_canceled(ctx))
 207                         return -ECANCELED;
 208         }
 209         return 0;
 210 }
 211
 212 static int timerfd_release(struct inode *inode, struct file *file)
 213 {
 214         struct timerfd_ctx *ctx = file->private_data;
 215
 216         timerfd_remove_cancel(ctx);
 217
 218         if (isalarm(ctx))
 219                 alarm_cancel(&ctx->t.alarm);
 220         else
 221                 hrtimer_cancel(&ctx->t.tmr);
 222         kfree_rcu(ctx, rcu);
 223         return 0;
 224 }
 225
 226 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
 227 {
 228         struct timerfd_ctx *ctx = file->private_data;
 229         unsigned int events = 0;
 230         unsigned long flags;
 231
 232         poll_wait(file, &ctx->wqh, wait);
 233
 234         spin_lock_irqsave(&ctx->wqh.lock, flags);
 235         if (ctx->ticks)
 236                 events |= POLLIN;
 237         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 238
 239         return events;
 240 }
 241
 242 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
 243                             loff_t *ppos)
 244 {
 245         struct timerfd_ctx *ctx = file->private_data;
 246         ssize_t res;
 247         u64 ticks = 0;
 248
 249         if (count < sizeof(ticks))
 250                 return -EINVAL;
 251         spin_lock_irq(&ctx->wqh.lock);
 252         if (file->f_flags & O_NONBLOCK)
 253                 res = -EAGAIN;
 254         else
 255                 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
 256
 257         /*
 258          * If clock has changed, we do not care about the
 259          * ticks and we do not rearm the timer. Userspace must
 260          * reevaluate anyway.
 261          */
 262         if (timerfd_canceled(ctx)) {
 263                 ctx->ticks = 0;
 264                 ctx->expired = 0;
 265                 res = -ECANCELED;
 266         }
 267
 268         if (ctx->ticks) {
 269                 ticks = ctx->ticks;
 270
 271                 if (ctx->expired && ctx->tintv.tv64) {
 272                         /*
 273                          * If tintv.tv64 != 0, this is a periodic timer that
 274                          * needs to be re-armed. We avoid doing it in the timer
 275                          * callback to avoid DoS attacks specifying a very
 276                          * short timer period.
 277                          */
 278                         if (isalarm(ctx)) {
 279                                 ticks += alarm_forward_now(
 280                                         &ctx->t.alarm, ctx->tintv) - 1;
 281                                 alarm_restart(&ctx->t.alarm);
 282                         } else {
 283                                 ticks += hrtimer_forward_now(&ctx->t.tmr,
 284                                                              ctx->tintv) - 1;
 285                                 hrtimer_restart(&ctx->t.tmr);
 286                         }
 287                 }
 288                 ctx->expired = 0;
 289                 ctx->ticks = 0;
 290         }
 291         spin_unlock_irq(&ctx->wqh.lock);
 292         if (ticks)
 293                 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
 294         return res;
 295 }
 296
 297 static const struct file_operations timerfd_fops = {
 298         .release        = timerfd_release,
 299         .poll           = timerfd_poll,
 300         .read           = timerfd_read,
 301         .llseek         = noop_llseek,
 302 };
 303
 304 static int timerfd_fget(int fd, struct fd *p)
 305 {
 306         struct fd f = fdget(fd);
 307         if (!f.file)
 308                 return -EBADF;
 309         if (f.file->f_op != &timerfd_fops) {
 310                 fdput(f);
 311                 return -EINVAL;
 312         }
 313         *p = f;
 314         return 0;
 315 }
 316
 317 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 318 {
 319         int ufd;
 320         struct timerfd_ctx *ctx;
 321
 322         /* Check the TFD_* constants for consistency.  */
 323         BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
 324         BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
 325
 326         if ((flags & ~TFD_CREATE_FLAGS) ||
 327             (clockid != CLOCK_MONOTONIC &&
 328              clockid != CLOCK_REALTIME &&
 329              clockid != CLOCK_REALTIME_ALARM &&
 330              clockid != CLOCK_BOOTTIME &&
 331              clockid != CLOCK_BOOTTIME_ALARM))
 332                 return -EINVAL;
 333
 334         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 335         if (!ctx)
 336                 return -ENOMEM;
 337
 338         init_waitqueue_head(&ctx->wqh);
 339         spin_lock_init(&ctx->cancel_lock);
 340         ctx->clockid = clockid;
 341
 342         if (isalarm(ctx))
 343                 alarm_init(&ctx->t.alarm,
 344                            ctx->clockid == CLOCK_REALTIME_ALARM ?
 345                            ALARM_REALTIME : ALARM_BOOTTIME,
 346                            timerfd_alarmproc);
 347         else
 348                 hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
 349
 350         ctx->moffs = ktime_get_monotonic_offset();
 351
 352         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
 353                                O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
 354         if (ufd < 0)
 355                 kfree(ctx);
 356
 357         return ufd;
 358 }
 359
 360 static int do_timerfd_settime(int ufd, int flags,
 361                 const struct itimerspec *new,
 362                 struct itimerspec *old)
 363 {
 364         struct fd f;
 365         struct timerfd_ctx *ctx;
 366         int ret;
 367
 368         if ((flags & ~TFD_SETTIME_FLAGS) ||
 369             !timespec_valid(&new->it_value) ||
 370             !timespec_valid(&new->it_interval))
 371                 return -EINVAL;
 372
 373         ret = timerfd_fget(ufd, &f);
 374         if (ret)
 375                 return ret;
 376         ctx = f.file->private_data;
 377
 378         timerfd_setup_cancel(ctx, flags);
 379
 380         /*
 381          * We need to stop the existing timer before reprogramming
 382          * it to the new values.
 383          */
 384         for (;;) {
 385                 spin_lock_irq(&ctx->wqh.lock);
 386
 387                 if (isalarm(ctx)) {
 388                         if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
 389                                 break;
 390                 } else {
 391                         if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
 392                                 break;
 393                 }
 394                 spin_unlock_irq(&ctx->wqh.lock);
 395                 cpu_relax();
 396         }
 397
 398         /*
 399          * If the timer is expired and it's periodic, we need to advance it
 400          * because the caller may want to know the previous expiration time.
 401          * We do not update "ticks" and "expired" since the timer will be
 402          * re-programmed again in the following timerfd_setup() call.
 403          */
 404         if (ctx->expired && ctx->tintv.tv64) {
 405                 if (isalarm(ctx))
 406                         alarm_forward_now(&ctx->t.alarm, ctx->tintv);
 407                 else
 408                         hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
 409         }
 410
 411         old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 412         old->it_interval = ktime_to_timespec(ctx->tintv);
 413
 414         /*
 415          * Re-program the timer to the new value ...
 416          */
 417         ret = timerfd_setup(ctx, flags, new);
 418
 419         spin_unlock_irq(&ctx->wqh.lock);
 420         fdput(f);
 421         return ret;
 422 }
 423
 424 static int do_timerfd_gettime(int ufd, struct itimerspec *t)
 425 {
 426         struct fd f;
 427         struct timerfd_ctx *ctx;
 428         int ret = timerfd_fget(ufd, &f);
 429         if (ret)
 430                 return ret;
 431         ctx = f.file->private_data;
 432
 433         spin_lock_irq(&ctx->wqh.lock);
 434         if (ctx->expired && ctx->tintv.tv64) {
 435                 ctx->expired = 0;
 436
 437                 if (isalarm(ctx)) {
 438                         ctx->ticks +=
 439                                 alarm_forward_now(
 440                                         &ctx->t.alarm, ctx->tintv) - 1;
 441                         alarm_restart(&ctx->t.alarm);
 442                 } else {
 443                         ctx->ticks +=
 444                                 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
 445                                 - 1;
 446                         hrtimer_restart(&ctx->t.tmr);
 447                 }
 448         }
 449         t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 450         t->it_interval = ktime_to_timespec(ctx->tintv);
 451         spin_unlock_irq(&ctx->wqh.lock);
 452         fdput(f);
 453         return 0;
 454 }
 455
 456 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 457                 const struct itimerspec __user *, utmr,
 458                 struct itimerspec __user *, otmr)
 459 {
 460         struct itimerspec new, old;
 461         int ret;
 462
 463         if (copy_from_user(&new, utmr, sizeof(new)))
 464                 return -EFAULT;
 465         ret = do_timerfd_settime(ufd, flags, &new, &old);
 466         if (ret)
 467                 return ret;
 468         if (otmr && copy_to_user(otmr, &old, sizeof(old)))
 469                 return -EFAULT;
 470
 471         return ret;
 472 }
 473
 474 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
 475 {
 476         struct itimerspec kotmr;
 477         int ret = do_timerfd_gettime(ufd, &kotmr);
 478         if (ret)
 479                 return ret;
 480         return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
 481 }
 482
 483 #ifdef CONFIG_COMPAT
 484 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 485                 const struct compat_itimerspec __user *, utmr,
 486                 struct compat_itimerspec __user *, otmr)
 487 {
 488         struct itimerspec new, old;
 489         int ret;
 490
 491         if (get_compat_itimerspec(&new, utmr))
 492                 return -EFAULT;
 493         ret = do_timerfd_settime(ufd, flags, &new, &old);
 494         if (ret)
 495                 return ret;
 496         if (otmr && put_compat_itimerspec(otmr, &old))
 497                 return -EFAULT;
 498         return ret;
 499 }
 500
 501 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
 502                 struct compat_itimerspec __user *, otmr)
 503 {
 504         struct itimerspec kotmr;
 505         int ret = do_timerfd_gettime(ufd, &kotmr);
 506         if (ret)
 507                 return ret;
 508         return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
 509 }
 510 #endif