xref: /openbmc/linux/fs/timerfd.c (revision 94c7b6fc) 
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 expired;
39 	int clockid;
40 	struct rcu_head rcu;
41 	struct list_head clist;
42 	bool might_cancel;
43 };
44 
45 static LIST_HEAD(cancel_list);
46 static DEFINE_SPINLOCK(cancel_lock);
47 
48 static inline bool isalarm(struct timerfd_ctx *ctx)
49 {
50 	return ctx->clockid == CLOCK_REALTIME_ALARM ||
51 		ctx->clockid == CLOCK_BOOTTIME_ALARM;
52 }
53 
54 /*
55  * This gets called when the timer event triggers. We set the "expired"
56  * flag, but we do not re-arm the timer (in case it's necessary,
57  * tintv.tv64 != 0) until the timer is accessed.
58  */
59 static void timerfd_triggered(struct timerfd_ctx *ctx)
60 {
61 	unsigned long flags;
62 
63 	spin_lock_irqsave(&ctx->wqh.lock, flags);
64 	ctx->expired = 1;
65 	ctx->ticks++;
66 	wake_up_locked(&ctx->wqh);
67 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
68 }
69 
70 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
71 {
72 	struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
73 					       t.tmr);
74 	timerfd_triggered(ctx);
75 	return HRTIMER_NORESTART;
76 }
77 
78 static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
79 	ktime_t now)
80 {
81 	struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
82 					       t.alarm);
83 	timerfd_triggered(ctx);
84 	return ALARMTIMER_NORESTART;
85 }
86 
87 /*
88  * Called when the clock was set to cancel the timers in the cancel
89  * list. This will wake up processes waiting on these timers. The
90  * wake-up requires ctx->ticks to be non zero, therefore we increment
91  * it before calling wake_up_locked().
92  */
93 void timerfd_clock_was_set(void)
94 {
95 	ktime_t moffs = ktime_get_monotonic_offset();
96 	struct timerfd_ctx *ctx;
97 	unsigned long flags;
98 
99 	rcu_read_lock();
100 	list_for_each_entry_rcu(ctx, &cancel_list, clist) {
101 		if (!ctx->might_cancel)
102 			continue;
103 		spin_lock_irqsave(&ctx->wqh.lock, flags);
104 		if (ctx->moffs.tv64 != moffs.tv64) {
105 			ctx->moffs.tv64 = KTIME_MAX;
106 			ctx->ticks++;
107 			wake_up_locked(&ctx->wqh);
108 		}
109 		spin_unlock_irqrestore(&ctx->wqh.lock, flags);
110 	}
111 	rcu_read_unlock();
112 }
113 
114 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
115 {
116 	if (ctx->might_cancel) {
117 		ctx->might_cancel = false;
118 		spin_lock(&cancel_lock);
119 		list_del_rcu(&ctx->clist);
120 		spin_unlock(&cancel_lock);
121 	}
122 }
123 
124 static bool timerfd_canceled(struct timerfd_ctx *ctx)
125 {
126 	if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
127 		return false;
128 	ctx->moffs = ktime_get_monotonic_offset();
129 	return true;
130 }
131 
132 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
133 {
134 	if ((ctx->clockid == CLOCK_REALTIME ||
135 	     ctx->clockid == CLOCK_REALTIME_ALARM) &&
136 	    (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
137 		if (!ctx->might_cancel) {
138 			ctx->might_cancel = true;
139 			spin_lock(&cancel_lock);
140 			list_add_rcu(&ctx->clist, &cancel_list);
141 			spin_unlock(&cancel_lock);
142 		}
143 	} else if (ctx->might_cancel) {
144 		timerfd_remove_cancel(ctx);
145 	}
146 }
147 
148 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
149 {
150 	ktime_t remaining;
151 
152 	if (isalarm(ctx))
153 		remaining = alarm_expires_remaining(&ctx->t.alarm);
154 	else
155 		remaining = hrtimer_expires_remaining(&ctx->t.tmr);
156 
157 	return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
158 }
159 
160 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
161 			 const struct itimerspec *ktmr)
162 {
163 	enum hrtimer_mode htmode;
164 	ktime_t texp;
165 	int clockid = ctx->clockid;
166 
167 	htmode = (flags & TFD_TIMER_ABSTIME) ?
168 		HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
169 
170 	texp = timespec_to_ktime(ktmr->it_value);
171 	ctx->expired = 0;
172 	ctx->ticks = 0;
173 	ctx->tintv = timespec_to_ktime(ktmr->it_interval);
174 
175 	if (isalarm(ctx)) {
176 		alarm_init(&ctx->t.alarm,
177 			   ctx->clockid == CLOCK_REALTIME_ALARM ?
178 			   ALARM_REALTIME : ALARM_BOOTTIME,
179 			   timerfd_alarmproc);
180 	} else {
181 		hrtimer_init(&ctx->t.tmr, clockid, htmode);
182 		hrtimer_set_expires(&ctx->t.tmr, texp);
183 		ctx->t.tmr.function = timerfd_tmrproc;
184 	}
185 
186 	if (texp.tv64 != 0) {
187 		if (isalarm(ctx)) {
188 			if (flags & TFD_TIMER_ABSTIME)
189 				alarm_start(&ctx->t.alarm, texp);
190 			else
191 				alarm_start_relative(&ctx->t.alarm, texp);
192 		} else {
193 			hrtimer_start(&ctx->t.tmr, texp, htmode);
194 		}
195 
196 		if (timerfd_canceled(ctx))
197 			return -ECANCELED;
198 	}
199 	return 0;
200 }
201 
202 static int timerfd_release(struct inode *inode, struct file *file)
203 {
204 	struct timerfd_ctx *ctx = file->private_data;
205 
206 	timerfd_remove_cancel(ctx);
207 
208 	if (isalarm(ctx))
209 		alarm_cancel(&ctx->t.alarm);
210 	else
211 		hrtimer_cancel(&ctx->t.tmr);
212 	kfree_rcu(ctx, rcu);
213 	return 0;
214 }
215 
216 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
217 {
218 	struct timerfd_ctx *ctx = file->private_data;
219 	unsigned int events = 0;
220 	unsigned long flags;
221 
222 	poll_wait(file, &ctx->wqh, wait);
223 
224 	spin_lock_irqsave(&ctx->wqh.lock, flags);
225 	if (ctx->ticks)
226 		events |= POLLIN;
227 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
228 
229 	return events;
230 }
231 
232 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
233 			    loff_t *ppos)
234 {
235 	struct timerfd_ctx *ctx = file->private_data;
236 	ssize_t res;
237 	u64 ticks = 0;
238 
239 	if (count < sizeof(ticks))
240 		return -EINVAL;
241 	spin_lock_irq(&ctx->wqh.lock);
242 	if (file->f_flags & O_NONBLOCK)
243 		res = -EAGAIN;
244 	else
245 		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
246 
247 	/*
248 	 * If clock has changed, we do not care about the
249 	 * ticks and we do not rearm the timer. Userspace must
250 	 * reevaluate anyway.
251 	 */
252 	if (timerfd_canceled(ctx)) {
253 		ctx->ticks = 0;
254 		ctx->expired = 0;
255 		res = -ECANCELED;
256 	}
257 
258 	if (ctx->ticks) {
259 		ticks = ctx->ticks;
260 
261 		if (ctx->expired && ctx->tintv.tv64) {
262 			/*
263 			 * If tintv.tv64 != 0, this is a periodic timer that
264 			 * needs to be re-armed. We avoid doing it in the timer
265 			 * callback to avoid DoS attacks specifying a very
266 			 * short timer period.
267 			 */
268 			if (isalarm(ctx)) {
269 				ticks += alarm_forward_now(
270 					&ctx->t.alarm, ctx->tintv) - 1;
271 				alarm_restart(&ctx->t.alarm);
272 			} else {
273 				ticks += hrtimer_forward_now(&ctx->t.tmr,
274 							     ctx->tintv) - 1;
275 				hrtimer_restart(&ctx->t.tmr);
276 			}
277 		}
278 		ctx->expired = 0;
279 		ctx->ticks = 0;
280 	}
281 	spin_unlock_irq(&ctx->wqh.lock);
282 	if (ticks)
283 		res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
284 	return res;
285 }
286 
287 static const struct file_operations timerfd_fops = {
288 	.release	= timerfd_release,
289 	.poll		= timerfd_poll,
290 	.read		= timerfd_read,
291 	.llseek		= noop_llseek,
292 };
293 
294 static int timerfd_fget(int fd, struct fd *p)
295 {
296 	struct fd f = fdget(fd);
297 	if (!f.file)
298 		return -EBADF;
299 	if (f.file->f_op != &timerfd_fops) {
300 		fdput(f);
301 		return -EINVAL;
302 	}
303 	*p = f;
304 	return 0;
305 }
306 
307 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
308 {
309 	int ufd;
310 	struct timerfd_ctx *ctx;
311 
312 	/* Check the TFD_* constants for consistency.  */
313 	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
314 	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
315 
316 	if ((flags & ~TFD_CREATE_FLAGS) ||
317 	    (clockid != CLOCK_MONOTONIC &&
318 	     clockid != CLOCK_REALTIME &&
319 	     clockid != CLOCK_REALTIME_ALARM &&
320 	     clockid != CLOCK_BOOTTIME &&
321 	     clockid != CLOCK_BOOTTIME_ALARM))
322 		return -EINVAL;
323 
324 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
325 	if (!ctx)
326 		return -ENOMEM;
327 
328 	init_waitqueue_head(&ctx->wqh);
329 	ctx->clockid = clockid;
330 
331 	if (isalarm(ctx))
332 		alarm_init(&ctx->t.alarm,
333 			   ctx->clockid == CLOCK_REALTIME_ALARM ?
334 			   ALARM_REALTIME : ALARM_BOOTTIME,
335 			   timerfd_alarmproc);
336 	else
337 		hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
338 
339 	ctx->moffs = ktime_get_monotonic_offset();
340 
341 	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
342 			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
343 	if (ufd < 0)
344 		kfree(ctx);
345 
346 	return ufd;
347 }
348 
349 static int do_timerfd_settime(int ufd, int flags,
350 		const struct itimerspec *new,
351 		struct itimerspec *old)
352 {
353 	struct fd f;
354 	struct timerfd_ctx *ctx;
355 	int ret;
356 
357 	if ((flags & ~TFD_SETTIME_FLAGS) ||
358 	    !timespec_valid(&new->it_value) ||
359 	    !timespec_valid(&new->it_interval))
360 		return -EINVAL;
361 
362 	ret = timerfd_fget(ufd, &f);
363 	if (ret)
364 		return ret;
365 	ctx = f.file->private_data;
366 
367 	timerfd_setup_cancel(ctx, flags);
368 
369 	/*
370 	 * We need to stop the existing timer before reprogramming
371 	 * it to the new values.
372 	 */
373 	for (;;) {
374 		spin_lock_irq(&ctx->wqh.lock);
375 
376 		if (isalarm(ctx)) {
377 			if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
378 				break;
379 		} else {
380 			if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
381 				break;
382 		}
383 		spin_unlock_irq(&ctx->wqh.lock);
384 		cpu_relax();
385 	}
386 
387 	/*
388 	 * If the timer is expired and it's periodic, we need to advance it
389 	 * because the caller may want to know the previous expiration time.
390 	 * We do not update "ticks" and "expired" since the timer will be
391 	 * re-programmed again in the following timerfd_setup() call.
392 	 */
393 	if (ctx->expired && ctx->tintv.tv64) {
394 		if (isalarm(ctx))
395 			alarm_forward_now(&ctx->t.alarm, ctx->tintv);
396 		else
397 			hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
398 	}
399 
400 	old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
401 	old->it_interval = ktime_to_timespec(ctx->tintv);
402 
403 	/*
404 	 * Re-program the timer to the new value ...
405 	 */
406 	ret = timerfd_setup(ctx, flags, new);
407 
408 	spin_unlock_irq(&ctx->wqh.lock);
409 	fdput(f);
410 	return ret;
411 }
412 
413 static int do_timerfd_gettime(int ufd, struct itimerspec *t)
414 {
415 	struct fd f;
416 	struct timerfd_ctx *ctx;
417 	int ret = timerfd_fget(ufd, &f);
418 	if (ret)
419 		return ret;
420 	ctx = f.file->private_data;
421 
422 	spin_lock_irq(&ctx->wqh.lock);
423 	if (ctx->expired && ctx->tintv.tv64) {
424 		ctx->expired = 0;
425 
426 		if (isalarm(ctx)) {
427 			ctx->ticks +=
428 				alarm_forward_now(
429 					&ctx->t.alarm, ctx->tintv) - 1;
430 			alarm_restart(&ctx->t.alarm);
431 		} else {
432 			ctx->ticks +=
433 				hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
434 				- 1;
435 			hrtimer_restart(&ctx->t.tmr);
436 		}
437 	}
438 	t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
439 	t->it_interval = ktime_to_timespec(ctx->tintv);
440 	spin_unlock_irq(&ctx->wqh.lock);
441 	fdput(f);
442 	return 0;
443 }
444 
445 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
446 		const struct itimerspec __user *, utmr,
447 		struct itimerspec __user *, otmr)
448 {
449 	struct itimerspec new, old;
450 	int ret;
451 
452 	if (copy_from_user(&new, utmr, sizeof(new)))
453 		return -EFAULT;
454 	ret = do_timerfd_settime(ufd, flags, &new, &old);
455 	if (ret)
456 		return ret;
457 	if (otmr && copy_to_user(otmr, &old, sizeof(old)))
458 		return -EFAULT;
459 
460 	return ret;
461 }
462 
463 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
464 {
465 	struct itimerspec kotmr;
466 	int ret = do_timerfd_gettime(ufd, &kotmr);
467 	if (ret)
468 		return ret;
469 	return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
470 }
471 
472 #ifdef CONFIG_COMPAT
473 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
474 		const struct compat_itimerspec __user *, utmr,
475 		struct compat_itimerspec __user *, otmr)
476 {
477 	struct itimerspec new, old;
478 	int ret;
479 
480 	if (get_compat_itimerspec(&new, utmr))
481 		return -EFAULT;
482 	ret = do_timerfd_settime(ufd, flags, &new, &old);
483 	if (ret)
484 		return ret;
485 	if (otmr && put_compat_itimerspec(otmr, &old))
486 		return -EFAULT;
487 	return ret;
488 }
489 
490 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
491 		struct compat_itimerspec __user *, otmr)
492 {
493 	struct itimerspec kotmr;
494 	int ret = do_timerfd_gettime(ufd, &kotmr);
495 	if (ret)
496 		return ret;
497 	return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
498 }
499 #endif
500