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/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
  27 struct 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
  40 static LIST_HEAD(cancel_list);
  41 static 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  */
  48 static 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  */
  68 void 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
  89 static 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
  99 static 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
 107 static 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
 122 static 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
 130 static 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
 155 static 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
 165 static 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
 181 static 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
 230 static const struct file_operations timerfd_fops = {
 231         .release        = timerfd_release,
 232         .poll           = timerfd_poll,
 233         .read           = timerfd_read,
 234         .llseek         = noop_llseek,
 235 };
 236
 237 static 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
 252 SYSCALL_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
 283 SYSCALL_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
 344 SYSCALL_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