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/list.h>
  18 #include <linux/spinlock.h>
  19 #include <linux/time.h>
  20 #include <linux/hrtimer.h>
  21 #include <linux/anon_inodes.h>
  22 #include <linux/timerfd.h>
  23
  24 struct timerfd_ctx {
  25         struct hrtimer tmr;
  26         ktime_t tintv;
  27         spinlock_t lock;
  28         wait_queue_head_t wqh;
  29         int expired;
  30 };
  31
  32 /*
  33  * This gets called when the timer event triggers. We set the "expired"
  34  * flag, but we do not re-arm the timer (in case it's necessary,
  35  * tintv.tv64 != 0) until the timer is read.
  36  */
  37 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
  38 {
  39         struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
  40         unsigned long flags;
  41
  42         spin_lock_irqsave(&ctx->lock, flags);
  43         ctx->expired = 1;
  44         wake_up_locked(&ctx->wqh);
  45         spin_unlock_irqrestore(&ctx->lock, flags);
  46
  47         return HRTIMER_NORESTART;
  48 }
  49
  50 static void timerfd_setup(struct timerfd_ctx *ctx, int clockid, int flags,
  51                           const struct itimerspec *ktmr)
  52 {
  53         enum hrtimer_mode htmode;
  54         ktime_t texp;
  55
  56         htmode = (flags & TFD_TIMER_ABSTIME) ?
  57                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
  58
  59         texp = timespec_to_ktime(ktmr->it_value);
  60         ctx->expired = 0;
  61         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
  62         hrtimer_init(&ctx->tmr, clockid, htmode);
  63         ctx->tmr.expires = texp;
  64         ctx->tmr.function = timerfd_tmrproc;
  65         if (texp.tv64 != 0)
  66                 hrtimer_start(&ctx->tmr, texp, htmode);
  67 }
  68
  69 static int timerfd_release(struct inode *inode, struct file *file)
  70 {
  71         struct timerfd_ctx *ctx = file->private_data;
  72
  73         hrtimer_cancel(&ctx->tmr);
  74         kfree(ctx);
  75         return 0;
  76 }
  77
  78 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
  79 {
  80         struct timerfd_ctx *ctx = file->private_data;
  81         unsigned int events = 0;
  82         unsigned long flags;
  83
  84         poll_wait(file, &ctx->wqh, wait);
  85
  86         spin_lock_irqsave(&ctx->lock, flags);
  87         if (ctx->expired)
  88                 events |= POLLIN;
  89         spin_unlock_irqrestore(&ctx->lock, flags);
  90
  91         return events;
  92 }
  93
  94 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
  95                             loff_t *ppos)
  96 {
  97         struct timerfd_ctx *ctx = file->private_data;
  98         ssize_t res;
  99         u32 ticks = 0;
 100         DECLARE_WAITQUEUE(wait, current);
 101
 102         if (count < sizeof(ticks))
 103                 return -EINVAL;
 104         spin_lock_irq(&ctx->lock);
 105         res = -EAGAIN;
 106         if (!ctx->expired && !(file->f_flags & O_NONBLOCK)) {
 107                 __add_wait_queue(&ctx->wqh, &wait);
 108                 for (res = 0;;) {
 109                         set_current_state(TASK_INTERRUPTIBLE);
 110                         if (ctx->expired) {
 111                                 res = 0;
 112                                 break;
 113                         }
 114                         if (signal_pending(current)) {
 115                                 res = -ERESTARTSYS;
 116                                 break;
 117                         }
 118                         spin_unlock_irq(&ctx->lock);
 119                         schedule();
 120                         spin_lock_irq(&ctx->lock);
 121                 }
 122                 __remove_wait_queue(&ctx->wqh, &wait);
 123                 __set_current_state(TASK_RUNNING);
 124         }
 125         if (ctx->expired) {
 126                 ctx->expired = 0;
 127                 if (ctx->tintv.tv64 != 0) {
 128                         /*
 129                          * If tintv.tv64 != 0, this is a periodic timer that
 130                          * needs to be re-armed. We avoid doing it in the timer
 131                          * callback to avoid DoS attacks specifying a very
 132                          * short timer period.
 133                          */
 134                         ticks = (u32)
 135                                 hrtimer_forward(&ctx->tmr,
 136                                                 hrtimer_cb_get_time(&ctx->tmr),
 137                                                 ctx->tintv);
 138                         hrtimer_restart(&ctx->tmr);
 139                 } else
 140                         ticks = 1;
 141         }
 142         spin_unlock_irq(&ctx->lock);
 143         if (ticks)
 144                 res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks);
 145         return res;
 146 }
 147
 148 static const struct file_operations timerfd_fops = {
 149         .release        = timerfd_release,
 150         .poll           = timerfd_poll,
 151         .read           = timerfd_read,
 152 };
 153
 154 asmlinkage long sys_timerfd(int ufd, int clockid, int flags,
 155                             const struct itimerspec __user *utmr)
 156 {
 157         int error;
 158         struct timerfd_ctx *ctx;
 159         struct file *file;
 160         struct inode *inode;
 161         struct itimerspec ktmr;
 162
 163         if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
 164                 return -EFAULT;
 165
 166         if (clockid != CLOCK_MONOTONIC &&
 167             clockid != CLOCK_REALTIME)
 168                 return -EINVAL;
 169         if (!timespec_valid(&ktmr.it_value) ||
 170             !timespec_valid(&ktmr.it_interval))
 171                 return -EINVAL;
 172
 173         if (ufd == -1) {
 174                 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
 175                 if (!ctx)
 176                         return -ENOMEM;
 177
 178                 init_waitqueue_head(&ctx->wqh);
 179                 spin_lock_init(&ctx->lock);
 180
 181                 timerfd_setup(ctx, clockid, flags, &ktmr);
 182
 183                 /*
 184                  * When we call this, the initialization must be complete, since
 185                  * anon_inode_getfd() will install the fd.
 186                  */
 187                 error = anon_inode_getfd(&ufd, &inode, &file, "[timerfd]",
 188                                          &timerfd_fops, ctx);
 189                 if (error)
 190                         goto err_tmrcancel;
 191         } else {
 192                 file = fget(ufd);
 193                 if (!file)
 194                         return -EBADF;
 195                 ctx = file->private_data;
 196                 if (file->f_op != &timerfd_fops) {
 197                         fput(file);
 198                         return -EINVAL;
 199                 }
 200                 /*
 201                  * We need to stop the existing timer before reprogramming
 202                  * it to the new values.
 203                  */
 204                 for (;;) {
 205                         spin_lock_irq(&ctx->lock);
 206                         if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
 207                                 break;
 208                         spin_unlock_irq(&ctx->lock);
 209                         cpu_relax();
 210                 }
 211                 /*
 212                  * Re-program the timer to the new value ...
 213                  */
 214                 timerfd_setup(ctx, clockid, flags, &ktmr);
 215
 216                 spin_unlock_irq(&ctx->lock);
 217                 fput(file);
 218         }
 219
 220         return ufd;
 221
 222 err_tmrcancel:
 223         hrtimer_cancel(&ctx->tmr);
 224         kfree(ctx);
 225         return error;
 226 }
 227