linux/fs/timerfd.c
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   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
  29struct 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
  45static LIST_HEAD(cancel_list);
  46static DEFINE_SPINLOCK(cancel_lock);
  47
  48static 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 */
  59static 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
  70static 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
  78static 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 */
  93void 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
 114static 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
 124static 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
 132static 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
 148static 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
 160static 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
 202static 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
 216static 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
 232static 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
 287static const struct file_operations timerfd_fops = {
 288        .release        = timerfd_release,
 289        .poll           = timerfd_poll,
 290        .read           = timerfd_read,
 291        .llseek         = noop_llseek,
 292};
 293
 294static 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
 307SYSCALL_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_ALARM))
 321                return -EINVAL;
 322
 323        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 324        if (!ctx)
 325                return -ENOMEM;
 326
 327        init_waitqueue_head(&ctx->wqh);
 328        ctx->clockid = clockid;
 329
 330        if (isalarm(ctx))
 331                alarm_init(&ctx->t.alarm,
 332                           ctx->clockid == CLOCK_REALTIME_ALARM ?
 333                           ALARM_REALTIME : ALARM_BOOTTIME,
 334                           timerfd_alarmproc);
 335        else
 336                hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
 337
 338        ctx->moffs = ktime_get_monotonic_offset();
 339
 340        ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
 341                               O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
 342        if (ufd < 0)
 343                kfree(ctx);
 344
 345        return ufd;
 346}
 347
 348static int do_timerfd_settime(int ufd, int flags, 
 349                const struct itimerspec *new,
 350                struct itimerspec *old)
 351{
 352        struct fd f;
 353        struct timerfd_ctx *ctx;
 354        int ret;
 355
 356        if ((flags & ~TFD_SETTIME_FLAGS) ||
 357            !timespec_valid(&new->it_value) ||
 358            !timespec_valid(&new->it_interval))
 359                return -EINVAL;
 360
 361        ret = timerfd_fget(ufd, &f);
 362        if (ret)
 363                return ret;
 364        ctx = f.file->private_data;
 365
 366        timerfd_setup_cancel(ctx, flags);
 367
 368        /*
 369         * We need to stop the existing timer before reprogramming
 370         * it to the new values.
 371         */
 372        for (;;) {
 373                spin_lock_irq(&ctx->wqh.lock);
 374
 375                if (isalarm(ctx)) {
 376                        if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
 377                                break;
 378                } else {
 379                        if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
 380                                break;
 381                }
 382                spin_unlock_irq(&ctx->wqh.lock);
 383                cpu_relax();
 384        }
 385
 386        /*
 387         * If the timer is expired and it's periodic, we need to advance it
 388         * because the caller may want to know the previous expiration time.
 389         * We do not update "ticks" and "expired" since the timer will be
 390         * re-programmed again in the following timerfd_setup() call.
 391         */
 392        if (ctx->expired && ctx->tintv.tv64) {
 393                if (isalarm(ctx))
 394                        alarm_forward_now(&ctx->t.alarm, ctx->tintv);
 395                else
 396                        hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
 397        }
 398
 399        old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 400        old->it_interval = ktime_to_timespec(ctx->tintv);
 401
 402        /*
 403         * Re-program the timer to the new value ...
 404         */
 405        ret = timerfd_setup(ctx, flags, new);
 406
 407        spin_unlock_irq(&ctx->wqh.lock);
 408        fdput(f);
 409        return ret;
 410}
 411
 412static int do_timerfd_gettime(int ufd, struct itimerspec *t)
 413{
 414        struct fd f;
 415        struct timerfd_ctx *ctx;
 416        int ret = timerfd_fget(ufd, &f);
 417        if (ret)
 418                return ret;
 419        ctx = f.file->private_data;
 420
 421        spin_lock_irq(&ctx->wqh.lock);
 422        if (ctx->expired && ctx->tintv.tv64) {
 423                ctx->expired = 0;
 424
 425                if (isalarm(ctx)) {
 426                        ctx->ticks +=
 427                                alarm_forward_now(
 428                                        &ctx->t.alarm, ctx->tintv) - 1;
 429                        alarm_restart(&ctx->t.alarm);
 430                } else {
 431                        ctx->ticks +=
 432                                hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
 433                                - 1;
 434                        hrtimer_restart(&ctx->t.tmr);
 435                }
 436        }
 437        t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 438        t->it_interval = ktime_to_timespec(ctx->tintv);
 439        spin_unlock_irq(&ctx->wqh.lock);
 440        fdput(f);
 441        return 0;
 442}
 443
 444SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 445                const struct itimerspec __user *, utmr,
 446                struct itimerspec __user *, otmr)
 447{
 448        struct itimerspec new, old;
 449        int ret;
 450
 451        if (copy_from_user(&new, utmr, sizeof(new)))
 452                return -EFAULT;
 453        ret = do_timerfd_settime(ufd, flags, &new, &old);
 454        if (ret)
 455                return ret;
 456        if (otmr && copy_to_user(otmr, &old, sizeof(old)))
 457                return -EFAULT;
 458
 459        return ret;
 460}
 461
 462SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
 463{
 464        struct itimerspec kotmr;
 465        int ret = do_timerfd_gettime(ufd, &kotmr);
 466        if (ret)
 467                return ret;
 468        return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
 469}
 470
 471#ifdef CONFIG_COMPAT
 472COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 473                const struct compat_itimerspec __user *, utmr,
 474                struct compat_itimerspec __user *, otmr)
 475{
 476        struct itimerspec new, old;
 477        int ret;
 478
 479        if (get_compat_itimerspec(&new, utmr))
 480                return -EFAULT;
 481        ret = do_timerfd_settime(ufd, flags, &new, &old);
 482        if (ret)
 483                return ret;
 484        if (otmr && put_compat_itimerspec(otmr, &old))
 485                return -EFAULT;
 486        return ret;
 487}
 488
 489COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
 490                struct compat_itimerspec __user *, otmr)
 491{
 492        struct itimerspec kotmr;
 493        int ret = do_timerfd_gettime(ufd, &kotmr);
 494        if (ret)
 495                return ret;
 496        return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
 497}
 498#endif
 499
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