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 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
46static LIST_HEAD(cancel_list);
47static DEFINE_SPINLOCK(cancel_lock);
48
49static 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.tv64 != 0) until the timer is accessed.
59 */
60static 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
71static 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
79static 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 */
94void timerfd_clock_was_set(void)
95{
96	ktime_t moffs = ktime_mono_to_real((ktime_t){ .tv64 = 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.tv64 != moffs.tv64) {
106			ctx->moffs.tv64 = 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
115static 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
125static bool timerfd_canceled(struct timerfd_ctx *ctx)
126{
127	if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
128		return false;
129	ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
130	return true;
131}
132
133static 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
149static 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(&ctx->t.tmr);
157
158	return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
159}
160
161static 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.tv64 != 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
205static 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
219static 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
235static 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.tv64) {
265			/*
266			 * If tintv.tv64 != 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
291static 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
320static 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
354static 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
363static 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
376SYSCALL_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	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
394	if (!ctx)
395		return -ENOMEM;
396
397	init_waitqueue_head(&ctx->wqh);
398	ctx->clockid = clockid;
399
400	if (isalarm(ctx))
401		alarm_init(&ctx->t.alarm,
402			   ctx->clockid == CLOCK_REALTIME_ALARM ?
403			   ALARM_REALTIME : ALARM_BOOTTIME,
404			   timerfd_alarmproc);
405	else
406		hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
407
408	ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 0 });
409
410	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
411			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
412	if (ufd < 0)
413		kfree(ctx);
414
415	return ufd;
416}
417
418static int do_timerfd_settime(int ufd, int flags,
419		const struct itimerspec *new,
420		struct itimerspec *old)
421{
422	struct fd f;
423	struct timerfd_ctx *ctx;
424	int ret;
425
426	if ((flags & ~TFD_SETTIME_FLAGS) ||
427	    !timespec_valid(&new->it_value) ||
428	    !timespec_valid(&new->it_interval))
429		return -EINVAL;
430
431	ret = timerfd_fget(ufd, &f);
432	if (ret)
433		return ret;
434	ctx = f.file->private_data;
435
436	timerfd_setup_cancel(ctx, flags);
437
438	/*
439	 * We need to stop the existing timer before reprogramming
440	 * it to the new values.
441	 */
442	for (;;) {
443		spin_lock_irq(&ctx->wqh.lock);
444
445		if (isalarm(ctx)) {
446			if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
447				break;
448		} else {
449			if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
450				break;
451		}
452		spin_unlock_irq(&ctx->wqh.lock);
453		cpu_relax();
454	}
455
456	/*
457	 * If the timer is expired and it's periodic, we need to advance it
458	 * because the caller may want to know the previous expiration time.
459	 * We do not update "ticks" and "expired" since the timer will be
460	 * re-programmed again in the following timerfd_setup() call.
461	 */
462	if (ctx->expired && ctx->tintv.tv64) {
463		if (isalarm(ctx))
464			alarm_forward_now(&ctx->t.alarm, ctx->tintv);
465		else
466			hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
467	}
468
469	old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
470	old->it_interval = ktime_to_timespec(ctx->tintv);
471
472	/*
473	 * Re-program the timer to the new value ...
474	 */
475	ret = timerfd_setup(ctx, flags, new);
476
477	spin_unlock_irq(&ctx->wqh.lock);
478	fdput(f);
479	return ret;
480}
481
482static int do_timerfd_gettime(int ufd, struct itimerspec *t)
483{
484	struct fd f;
485	struct timerfd_ctx *ctx;
486	int ret = timerfd_fget(ufd, &f);
487	if (ret)
488		return ret;
489	ctx = f.file->private_data;
490
491	spin_lock_irq(&ctx->wqh.lock);
492	if (ctx->expired && ctx->tintv.tv64) {
493		ctx->expired = 0;
494
495		if (isalarm(ctx)) {
496			ctx->ticks +=
497				alarm_forward_now(
498					&ctx->t.alarm, ctx->tintv) - 1;
499			alarm_restart(&ctx->t.alarm);
500		} else {
501			ctx->ticks +=
502				hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
503				- 1;
504			hrtimer_restart(&ctx->t.tmr);
505		}
506	}
507	t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
508	t->it_interval = ktime_to_timespec(ctx->tintv);
509	spin_unlock_irq(&ctx->wqh.lock);
510	fdput(f);
511	return 0;
512}
513
514SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
515		const struct itimerspec __user *, utmr,
516		struct itimerspec __user *, otmr)
517{
518	struct itimerspec new, old;
519	int ret;
520
521	if (copy_from_user(&new, utmr, sizeof(new)))
522		return -EFAULT;
523	ret = do_timerfd_settime(ufd, flags, &new, &old);
524	if (ret)
525		return ret;
526	if (otmr && copy_to_user(otmr, &old, sizeof(old)))
527		return -EFAULT;
528
529	return ret;
530}
531
532SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
533{
534	struct itimerspec kotmr;
535	int ret = do_timerfd_gettime(ufd, &kotmr);
536	if (ret)
537		return ret;
538	return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
539}
540
541#ifdef CONFIG_COMPAT
542COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
543		const struct compat_itimerspec __user *, utmr,
544		struct compat_itimerspec __user *, otmr)
545{
546	struct itimerspec new, old;
547	int ret;
548
549	if (get_compat_itimerspec(&new, utmr))
550		return -EFAULT;
551	ret = do_timerfd_settime(ufd, flags, &new, &old);
552	if (ret)
553		return ret;
554	if (otmr && put_compat_itimerspec(otmr, &old))
555		return -EFAULT;
556	return ret;
557}
558
559COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
560		struct compat_itimerspec __user *, otmr)
561{
562	struct itimerspec kotmr;
563	int ret = do_timerfd_gettime(ufd, &kotmr);
564	if (ret)
565		return ret;
566	return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
567}
568#endif
569