linux/fs/timerfd.c
<<
>>
Prefs
   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/file.h>
  12#include <linux/poll.h>
  13#include <linux/init.h>
  14#include <linux/fs.h>
  15#include <linux/sched.h>
  16#include <linux/kernel.h>
  17#include <linux/slab.h>
  18#include <linux/list.h>
  19#include <linux/spinlock.h>
  20#include <linux/time.h>
  21#include <linux/hrtimer.h>
  22#include <linux/anon_inodes.h>
  23#include <linux/timerfd.h>
  24#include <linux/syscalls.h>
  25#include <linux/rcupdate.h>
  26
  27struct timerfd_ctx {
  28        struct hrtimer tmr;
  29        ktime_t tintv;
  30        ktime_t moffs;
  31        wait_queue_head_t wqh;
  32        u64 ticks;
  33        int expired;
  34        int clockid;
  35        struct rcu_head rcu;
  36        struct list_head clist;
  37        bool might_cancel;
  38};
  39
  40static LIST_HEAD(cancel_list);
  41static DEFINE_SPINLOCK(cancel_lock);
  42
  43/*
  44 * This gets called when the timer event triggers. We set the "expired"
  45 * flag, but we do not re-arm the timer (in case it's necessary,
  46 * tintv.tv64 != 0) until the timer is accessed.
  47 */
  48static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
  49{
  50        struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
  51        unsigned long flags;
  52
  53        spin_lock_irqsave(&ctx->wqh.lock, flags);
  54        ctx->expired = 1;
  55        ctx->ticks++;
  56        wake_up_locked(&ctx->wqh);
  57        spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  58
  59        return HRTIMER_NORESTART;
  60}
  61
  62/*
  63 * Called when the clock was set to cancel the timers in the cancel
  64 * list. This will wake up processes waiting on these timers. The
  65 * wake-up requires ctx->ticks to be non zero, therefore we increment
  66 * it before calling wake_up_locked().
  67 */
  68void timerfd_clock_was_set(void)
  69{
  70        ktime_t moffs = ktime_get_monotonic_offset();
  71        struct timerfd_ctx *ctx;
  72        unsigned long flags;
  73
  74        rcu_read_lock();
  75        list_for_each_entry_rcu(ctx, &cancel_list, clist) {
  76                if (!ctx->might_cancel)
  77                        continue;
  78                spin_lock_irqsave(&ctx->wqh.lock, flags);
  79                if (ctx->moffs.tv64 != moffs.tv64) {
  80                        ctx->moffs.tv64 = KTIME_MAX;
  81                        ctx->ticks++;
  82                        wake_up_locked(&ctx->wqh);
  83                }
  84                spin_unlock_irqrestore(&ctx->wqh.lock, flags);
  85        }
  86        rcu_read_unlock();
  87}
  88
  89static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
  90{
  91        if (ctx->might_cancel) {
  92                ctx->might_cancel = false;
  93                spin_lock(&cancel_lock);
  94                list_del_rcu(&ctx->clist);
  95                spin_unlock(&cancel_lock);
  96        }
  97}
  98
  99static bool timerfd_canceled(struct timerfd_ctx *ctx)
 100{
 101        if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
 102                return false;
 103        ctx->moffs = ktime_get_monotonic_offset();
 104        return true;
 105}
 106
 107static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
 108{
 109        if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
 110            (flags & TFD_TIMER_CANCEL_ON_SET)) {
 111                if (!ctx->might_cancel) {
 112                        ctx->might_cancel = true;
 113                        spin_lock(&cancel_lock);
 114                        list_add_rcu(&ctx->clist, &cancel_list);
 115                        spin_unlock(&cancel_lock);
 116                }
 117        } else if (ctx->might_cancel) {
 118                timerfd_remove_cancel(ctx);
 119        }
 120}
 121
 122static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
 123{
 124        ktime_t remaining;
 125
 126        remaining = hrtimer_expires_remaining(&ctx->tmr);
 127        return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
 128}
 129
 130static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
 131                         const struct itimerspec *ktmr)
 132{
 133        enum hrtimer_mode htmode;
 134        ktime_t texp;
 135        int clockid = ctx->clockid;
 136
 137        htmode = (flags & TFD_TIMER_ABSTIME) ?
 138                HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
 139
 140        texp = timespec_to_ktime(ktmr->it_value);
 141        ctx->expired = 0;
 142        ctx->ticks = 0;
 143        ctx->tintv = timespec_to_ktime(ktmr->it_interval);
 144        hrtimer_init(&ctx->tmr, clockid, htmode);
 145        hrtimer_set_expires(&ctx->tmr, texp);
 146        ctx->tmr.function = timerfd_tmrproc;
 147        if (texp.tv64 != 0) {
 148                hrtimer_start(&ctx->tmr, texp, htmode);
 149                if (timerfd_canceled(ctx))
 150                        return -ECANCELED;
 151        }
 152        return 0;
 153}
 154
 155static int timerfd_release(struct inode *inode, struct file *file)
 156{
 157        struct timerfd_ctx *ctx = file->private_data;
 158
 159        timerfd_remove_cancel(ctx);
 160        hrtimer_cancel(&ctx->tmr);
 161        kfree_rcu(ctx, rcu);
 162        return 0;
 163}
 164
 165static unsigned int timerfd_poll(struct file *file, poll_table *wait)
 166{
 167        struct timerfd_ctx *ctx = file->private_data;
 168        unsigned int events = 0;
 169        unsigned long flags;
 170
 171        poll_wait(file, &ctx->wqh, wait);
 172
 173        spin_lock_irqsave(&ctx->wqh.lock, flags);
 174        if (ctx->ticks)
 175                events |= POLLIN;
 176        spin_unlock_irqrestore(&ctx->wqh.lock, flags);
 177
 178        return events;
 179}
 180
 181static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
 182                            loff_t *ppos)
 183{
 184        struct timerfd_ctx *ctx = file->private_data;
 185        ssize_t res;
 186        u64 ticks = 0;
 187
 188        if (count < sizeof(ticks))
 189                return -EINVAL;
 190        spin_lock_irq(&ctx->wqh.lock);
 191        if (file->f_flags & O_NONBLOCK)
 192                res = -EAGAIN;
 193        else
 194                res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
 195
 196        /*
 197         * If clock has changed, we do not care about the
 198         * ticks and we do not rearm the timer. Userspace must
 199         * reevaluate anyway.
 200         */
 201        if (timerfd_canceled(ctx)) {
 202                ctx->ticks = 0;
 203                ctx->expired = 0;
 204                res = -ECANCELED;
 205        }
 206
 207        if (ctx->ticks) {
 208                ticks = ctx->ticks;
 209
 210                if (ctx->expired && ctx->tintv.tv64) {
 211                        /*
 212                         * If tintv.tv64 != 0, this is a periodic timer that
 213                         * needs to be re-armed. We avoid doing it in the timer
 214                         * callback to avoid DoS attacks specifying a very
 215                         * short timer period.
 216                         */
 217                        ticks += hrtimer_forward_now(&ctx->tmr,
 218                                                     ctx->tintv) - 1;
 219                        hrtimer_restart(&ctx->tmr);
 220                }
 221                ctx->expired = 0;
 222                ctx->ticks = 0;
 223        }
 224        spin_unlock_irq(&ctx->wqh.lock);
 225        if (ticks)
 226                res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
 227        return res;
 228}
 229
 230static const struct file_operations timerfd_fops = {
 231        .release        = timerfd_release,
 232        .poll           = timerfd_poll,
 233        .read           = timerfd_read,
 234        .llseek         = noop_llseek,
 235};
 236
 237static struct file *timerfd_fget(int fd)
 238{
 239        struct file *file;
 240
 241        file = fget(fd);
 242        if (!file)
 243                return ERR_PTR(-EBADF);
 244        if (file->f_op != &timerfd_fops) {
 245                fput(file);
 246                return ERR_PTR(-EINVAL);
 247        }
 248
 249        return file;
 250}
 251
 252SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 253{
 254        int ufd;
 255        struct timerfd_ctx *ctx;
 256
 257        /* Check the TFD_* constants for consistency.  */
 258        BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
 259        BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
 260
 261        if ((flags & ~TFD_CREATE_FLAGS) ||
 262            (clockid != CLOCK_MONOTONIC &&
 263             clockid != CLOCK_REALTIME))
 264                return -EINVAL;
 265
 266        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 267        if (!ctx)
 268                return -ENOMEM;
 269
 270        init_waitqueue_head(&ctx->wqh);
 271        ctx->clockid = clockid;
 272        hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
 273        ctx->moffs = ktime_get_monotonic_offset();
 274
 275        ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
 276                               O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
 277        if (ufd < 0)
 278                kfree(ctx);
 279
 280        return ufd;
 281}
 282
 283SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
 284                const struct itimerspec __user *, utmr,
 285                struct itimerspec __user *, otmr)
 286{
 287        struct file *file;
 288        struct timerfd_ctx *ctx;
 289        struct itimerspec ktmr, kotmr;
 290        int ret;
 291
 292        if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
 293                return -EFAULT;
 294
 295        if ((flags & ~TFD_SETTIME_FLAGS) ||
 296            !timespec_valid(&ktmr.it_value) ||
 297            !timespec_valid(&ktmr.it_interval))
 298                return -EINVAL;
 299
 300        file = timerfd_fget(ufd);
 301        if (IS_ERR(file))
 302                return PTR_ERR(file);
 303        ctx = file->private_data;
 304
 305        timerfd_setup_cancel(ctx, flags);
 306
 307        /*
 308         * We need to stop the existing timer before reprogramming
 309         * it to the new values.
 310         */
 311        for (;;) {
 312                spin_lock_irq(&ctx->wqh.lock);
 313                if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
 314                        break;
 315                spin_unlock_irq(&ctx->wqh.lock);
 316                cpu_relax();
 317        }
 318
 319        /*
 320         * If the timer is expired and it's periodic, we need to advance it
 321         * because the caller may want to know the previous expiration time.
 322         * We do not update "ticks" and "expired" since the timer will be
 323         * re-programmed again in the following timerfd_setup() call.
 324         */
 325        if (ctx->expired && ctx->tintv.tv64)
 326                hrtimer_forward_now(&ctx->tmr, ctx->tintv);
 327
 328        kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 329        kotmr.it_interval = ktime_to_timespec(ctx->tintv);
 330
 331        /*
 332         * Re-program the timer to the new value ...
 333         */
 334        ret = timerfd_setup(ctx, flags, &ktmr);
 335
 336        spin_unlock_irq(&ctx->wqh.lock);
 337        fput(file);
 338        if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
 339                return -EFAULT;
 340
 341        return ret;
 342}
 343
 344SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
 345{
 346        struct file *file;
 347        struct timerfd_ctx *ctx;
 348        struct itimerspec kotmr;
 349
 350        file = timerfd_fget(ufd);
 351        if (IS_ERR(file))
 352                return PTR_ERR(file);
 353        ctx = file->private_data;
 354
 355        spin_lock_irq(&ctx->wqh.lock);
 356        if (ctx->expired && ctx->tintv.tv64) {
 357                ctx->expired = 0;
 358                ctx->ticks +=
 359                        hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
 360                hrtimer_restart(&ctx->tmr);
 361        }
 362        kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 363        kotmr.it_interval = ktime_to_timespec(ctx->tintv);
 364        spin_unlock_irq(&ctx->wqh.lock);
 365        fput(file);
 366
 367        return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
 368}
 369
 370
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.