xref: /openbmc/linux/fs/timerfd.c (revision eb3fcf00) 
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.tv64 != 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((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 
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.tv64 != KTIME_MAX)
128 		return false;
129 	ctx->moffs = ktime_mono_to_real((ktime_t){ .tv64 = 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(&ctx->t.tmr);
157 
158 	return remaining.tv64 < 0 ? ktime_set(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.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 
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.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
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 	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 
418 static 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 
482 static 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 
514 SYSCALL_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 
532 SYSCALL_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
542 COMPAT_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 
559 COMPAT_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