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Linux/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 clockid;
 39         short unsigned expired;
 40         short unsigned settime_flags;   /* to show in fdinfo */
 41         struct rcu_head rcu;
 42         struct list_head clist;
 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 != 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_mono_to_real(0);
 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 != moffs) {
106                         ctx->moffs = 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 bool timerfd_canceled(struct timerfd_ctx *ctx)
126 {
127         if (!ctx->might_cancel || ctx->moffs != KTIME_MAX)
128                 return false;
129         ctx->moffs = ktime_mono_to_real(0);
130         return true;
131 }
132 
133 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
134 {
135         if ((ctx->clockid == CLOCK_REALTIME ||
136              ctx->clockid == CLOCK_REALTIME_ALARM) &&
137             (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
138                 if (!ctx->might_cancel) {
139                         ctx->might_cancel = true;
140                         spin_lock(&cancel_lock);
141                         list_add_rcu(&ctx->clist, &cancel_list);
142                         spin_unlock(&cancel_lock);
143                 }
144         } else if (ctx->might_cancel) {
145                 timerfd_remove_cancel(ctx);
146         }
147 }
148 
149 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
150 {
151         ktime_t remaining;
152 
153         if (isalarm(ctx))
154                 remaining = alarm_expires_remaining(&ctx->t.alarm);
155         else
156                 remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
157 
158         return remaining < 0 ? 0: remaining;
159 }
160 
161 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
162                          const struct itimerspec *ktmr)
163 {
164         enum hrtimer_mode htmode;
165         ktime_t texp;
166         int clockid = ctx->clockid;
167 
168         htmode = (flags & TFD_TIMER_ABSTIME) ?
169                 HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
170 
171         texp = timespec_to_ktime(ktmr->it_value);
172         ctx->expired = 0;
173         ctx->ticks = 0;
174         ctx->tintv = timespec_to_ktime(ktmr->it_interval);
175 
176         if (isalarm(ctx)) {
177                 alarm_init(&ctx->t.alarm,
178                            ctx->clockid == CLOCK_REALTIME_ALARM ?
179                            ALARM_REALTIME : ALARM_BOOTTIME,
180                            timerfd_alarmproc);
181         } else {
182                 hrtimer_init(&ctx->t.tmr, clockid, htmode);
183                 hrtimer_set_expires(&ctx->t.tmr, texp);
184                 ctx->t.tmr.function = timerfd_tmrproc;
185         }
186 
187         if (texp != 0) {
188                 if (isalarm(ctx)) {
189                         if (flags & TFD_TIMER_ABSTIME)
190                                 alarm_start(&ctx->t.alarm, texp);
191                         else
192                                 alarm_start_relative(&ctx->t.alarm, texp);
193                 } else {
194                         hrtimer_start(&ctx->t.tmr, texp, htmode);
195                 }
196 
197                 if (timerfd_canceled(ctx))
198                         return -ECANCELED;
199         }
200 
201         ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
202         return 0;
203 }
204 
205 static int timerfd_release(struct inode *inode, struct file *file)
206 {
207         struct timerfd_ctx *ctx = file->private_data;
208 
209         timerfd_remove_cancel(ctx);
210 
211         if (isalarm(ctx))
212                 alarm_cancel(&ctx->t.alarm);
213         else
214                 hrtimer_cancel(&ctx->t.tmr);
215         kfree_rcu(ctx, rcu);
216         return 0;
217 }
218 
219 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
220 {
221         struct timerfd_ctx *ctx = file->private_data;
222         unsigned int events = 0;
223         unsigned long flags;
224 
225         poll_wait(file, &ctx->wqh, wait);
226 
227         spin_lock_irqsave(&ctx->wqh.lock, flags);
228         if (ctx->ticks)
229                 events |= POLLIN;
230         spin_unlock_irqrestore(&ctx->wqh.lock, flags);
231 
232         return events;
233 }
234 
235 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
236                             loff_t *ppos)
237 {
238         struct timerfd_ctx *ctx = file->private_data;
239         ssize_t res;
240         u64 ticks = 0;
241 
242         if (count < sizeof(ticks))
243                 return -EINVAL;
244         spin_lock_irq(&ctx->wqh.lock);
245         if (file->f_flags & O_NONBLOCK)
246                 res = -EAGAIN;
247         else
248                 res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
249 
250         /*
251          * If clock has changed, we do not care about the
252          * ticks and we do not rearm the timer. Userspace must
253          * reevaluate anyway.
254          */
255         if (timerfd_canceled(ctx)) {
256                 ctx->ticks = 0;
257                 ctx->expired = 0;
258                 res = -ECANCELED;
259         }
260 
261         if (ctx->ticks) {
262                 ticks = ctx->ticks;
263 
264                 if (ctx->expired && ctx->tintv) {
265                         /*
266                          * If tintv != 0, this is a periodic timer that
267                          * needs to be re-armed. We avoid doing it in the timer
268                          * callback to avoid DoS attacks specifying a very
269                          * short timer period.
270                          */
271                         if (isalarm(ctx)) {
272                                 ticks += alarm_forward_now(
273                                         &ctx->t.alarm, ctx->tintv) - 1;
274                                 alarm_restart(&ctx->t.alarm);
275                         } else {
276                                 ticks += hrtimer_forward_now(&ctx->t.tmr,
277                                                              ctx->tintv) - 1;
278                                 hrtimer_restart(&ctx->t.tmr);
279                         }
280                 }
281                 ctx->expired = 0;
282                 ctx->ticks = 0;
283         }
284         spin_unlock_irq(&ctx->wqh.lock);
285         if (ticks)
286                 res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
287         return res;
288 }
289 
290 #ifdef CONFIG_PROC_FS
291 static void timerfd_show(struct seq_file *m, struct file *file)
292 {
293         struct timerfd_ctx *ctx = file->private_data;
294         struct itimerspec t;
295 
296         spin_lock_irq(&ctx->wqh.lock);
297         t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
298         t.it_interval = ktime_to_timespec(ctx->tintv);
299         spin_unlock_irq(&ctx->wqh.lock);
300 
301         seq_printf(m,
302                    "clockid: %d\n"
303                    "ticks: %llu\n"
304                    "settime flags: 0%o\n"
305                    "it_value: (%llu, %llu)\n"
306                    "it_interval: (%llu, %llu)\n",
307                    ctx->clockid,
308                    (unsigned long long)ctx->ticks,
309                    ctx->settime_flags,
310                    (unsigned long long)t.it_value.tv_sec,
311                    (unsigned long long)t.it_value.tv_nsec,
312                    (unsigned long long)t.it_interval.tv_sec,
313                    (unsigned long long)t.it_interval.tv_nsec);
314 }
315 #else
316 #define timerfd_show NULL
317 #endif
318 
319 #ifdef CONFIG_CHECKPOINT_RESTORE
320 static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
321 {
322         struct timerfd_ctx *ctx = file->private_data;
323         int ret = 0;
324 
325         switch (cmd) {
326         case TFD_IOC_SET_TICKS: {
327                 u64 ticks;
328 
329                 if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
330                         return -EFAULT;
331                 if (!ticks)
332                         return -EINVAL;
333 
334                 spin_lock_irq(&ctx->wqh.lock);
335                 if (!timerfd_canceled(ctx)) {
336                         ctx->ticks = ticks;
337                         wake_up_locked(&ctx->wqh);
338                 } else
339                         ret = -ECANCELED;
340                 spin_unlock_irq(&ctx->wqh.lock);
341                 break;
342         }
343         default:
344                 ret = -ENOTTY;
345                 break;
346         }
347 
348         return ret;
349 }
350 #else
351 #define timerfd_ioctl NULL
352 #endif
353 
354 static const struct file_operations timerfd_fops = {
355         .release        = timerfd_release,
356         .poll           = timerfd_poll,
357         .read           = timerfd_read,
358         .llseek         = noop_llseek,
359         .show_fdinfo    = timerfd_show,
360         .unlocked_ioctl = timerfd_ioctl,
361 };
362 
363 static int timerfd_fget(int fd, struct fd *p)
364 {
365         struct fd f = fdget(fd);
366         if (!f.file)
367                 return -EBADF;
368         if (f.file->f_op != &timerfd_fops) {
369                 fdput(f);
370                 return -EINVAL;
371         }
372         *p = f;
373         return 0;
374 }
375 
376 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
377 {
378         int ufd;
379         struct timerfd_ctx *ctx;
380 
381         /* Check the TFD_* constants for consistency.  */
382         BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
383         BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
384 
385         if ((flags & ~TFD_CREATE_FLAGS) ||
386             (clockid != CLOCK_MONOTONIC &&
387              clockid != CLOCK_REALTIME &&
388              clockid != CLOCK_REALTIME_ALARM &&
389              clockid != CLOCK_BOOTTIME &&
390              clockid != CLOCK_BOOTTIME_ALARM))
391                 return -EINVAL;
392 
393         if (!capable(CAP_WAKE_ALARM) &&
394             (clockid == CLOCK_REALTIME_ALARM ||
395              clockid == CLOCK_BOOTTIME_ALARM))
396                 return -EPERM;
397 
398         ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
399         if (!ctx)
400                 return -ENOMEM;
401 
402         init_waitqueue_head(&ctx->wqh);
403         ctx->clockid = clockid;
404 
405         if (isalarm(ctx))
406                 alarm_init(&ctx->t.alarm,
407                            ctx->clockid == CLOCK_REALTIME_ALARM ?
408                            ALARM_REALTIME : ALARM_BOOTTIME,
409                            timerfd_alarmproc);
410         else
411                 hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
412 
413         ctx->moffs = ktime_mono_to_real(0);
414 
415         ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
416                                O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
417         if (ufd < 0)
418                 kfree(ctx);
419 
420         return ufd;
421 }
422 
423 static int do_timerfd_settime(int ufd, int flags, 
424                 const struct itimerspec *new,
425                 struct itimerspec *old)
426 {
427         struct fd f;
428         struct timerfd_ctx *ctx;
429         int ret;
430 
431         if ((flags & ~TFD_SETTIME_FLAGS) ||
432             !timespec_valid(&new->it_value) ||
433             !timespec_valid(&new->it_interval))
434                 return -EINVAL;
435 
436         ret = timerfd_fget(ufd, &f);
437         if (ret)
438                 return ret;
439         ctx = f.file->private_data;
440 
441         if (!capable(CAP_WAKE_ALARM) && isalarm(ctx)) {
442                 fdput(f);
443                 return -EPERM;
444         }
445 
446         timerfd_setup_cancel(ctx, flags);
447 
448         /*
449          * We need to stop the existing timer before reprogramming
450          * it to the new values.
451          */
452         for (;;) {
453                 spin_lock_irq(&ctx->wqh.lock);
454 
455                 if (isalarm(ctx)) {
456                         if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
457                                 break;
458                 } else {
459                         if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
460                                 break;
461                 }
462                 spin_unlock_irq(&ctx->wqh.lock);
463                 cpu_relax();
464         }
465 
466         /*
467          * If the timer is expired and it's periodic, we need to advance it
468          * because the caller may want to know the previous expiration time.
469          * We do not update "ticks" and "expired" since the timer will be
470          * re-programmed again in the following timerfd_setup() call.
471          */
472         if (ctx->expired && ctx->tintv) {
473                 if (isalarm(ctx))
474                         alarm_forward_now(&ctx->t.alarm, ctx->tintv);
475                 else
476                         hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
477         }
478 
479         old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
480         old->it_interval = ktime_to_timespec(ctx->tintv);
481 
482         /*
483          * Re-program the timer to the new value ...
484          */
485         ret = timerfd_setup(ctx, flags, new);
486 
487         spin_unlock_irq(&ctx->wqh.lock);
488         fdput(f);
489         return ret;
490 }
491 
492 static int do_timerfd_gettime(int ufd, struct itimerspec *t)
493 {
494         struct fd f;
495         struct timerfd_ctx *ctx;
496         int ret = timerfd_fget(ufd, &f);
497         if (ret)
498                 return ret;
499         ctx = f.file->private_data;
500 
501         spin_lock_irq(&ctx->wqh.lock);
502         if (ctx->expired && ctx->tintv) {
503                 ctx->expired = 0;
504 
505                 if (isalarm(ctx)) {
506                         ctx->ticks +=
507                                 alarm_forward_now(
508                                         &ctx->t.alarm, ctx->tintv) - 1;
509                         alarm_restart(&ctx->t.alarm);
510                 } else {
511                         ctx->ticks +=
512                                 hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
513                                 - 1;
514                         hrtimer_restart(&ctx->t.tmr);
515                 }
516         }
517         t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
518         t->it_interval = ktime_to_timespec(ctx->tintv);
519         spin_unlock_irq(&ctx->wqh.lock);
520         fdput(f);
521         return 0;
522 }
523 
524 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
525                 const struct itimerspec __user *, utmr,
526                 struct itimerspec __user *, otmr)
527 {
528         struct itimerspec new, old;
529         int ret;
530 
531         if (copy_from_user(&new, utmr, sizeof(new)))
532                 return -EFAULT;
533         ret = do_timerfd_settime(ufd, flags, &new, &old);
534         if (ret)
535                 return ret;
536         if (otmr && copy_to_user(otmr, &old, sizeof(old)))
537                 return -EFAULT;
538 
539         return ret;
540 }
541 
542 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
543 {
544         struct itimerspec kotmr;
545         int ret = do_timerfd_gettime(ufd, &kotmr);
546         if (ret)
547                 return ret;
548         return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
549 }
550 
551 #ifdef CONFIG_COMPAT
552 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
553                 const struct compat_itimerspec __user *, utmr,
554                 struct compat_itimerspec __user *, otmr)
555 {
556         struct itimerspec new, old;
557         int ret;
558 
559         if (get_compat_itimerspec(&new, utmr))
560                 return -EFAULT;
561         ret = do_timerfd_settime(ufd, flags, &new, &old);
562         if (ret)
563                 return ret;
564         if (otmr && put_compat_itimerspec(otmr, &old))
565                 return -EFAULT;
566         return ret;
567 }
568 
569 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
570                 struct compat_itimerspec __user *, otmr)
571 {
572         struct itimerspec kotmr;
573         int ret = do_timerfd_gettime(ufd, &kotmr);
574         if (ret)
575                 return ret;
576         return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
577 }
578 #endif
579 

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