projects/linux·blob v4.5 · refs

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1/*
2 * fs/timerfd.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <[email protected]>
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_adjusted(&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