xref: /openbmc/linux/fs/timerfd.c (revision 1dd24dae) 
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/file.h>
12 #include <linux/poll.h>
13 #include <linux/init.h>
14 #include <linux/fs.h>
15 #include <linux/sched.h>
16 #include <linux/kernel.h>
17 #include <linux/slab.h>
18 #include <linux/list.h>
19 #include <linux/spinlock.h>
20 #include <linux/time.h>
21 #include <linux/hrtimer.h>
22 #include <linux/anon_inodes.h>
23 #include <linux/timerfd.h>
24 #include <linux/syscalls.h>
25 #include <linux/compat.h>
26 #include <linux/rcupdate.h>
27 
28 struct timerfd_ctx {
29 	struct hrtimer tmr;
30 	ktime_t tintv;
31 	ktime_t moffs;
32 	wait_queue_head_t wqh;
33 	u64 ticks;
34 	int expired;
35 	int clockid;
36 	struct rcu_head rcu;
37 	struct list_head clist;
38 	bool might_cancel;
39 };
40 
41 static LIST_HEAD(cancel_list);
42 static DEFINE_SPINLOCK(cancel_lock);
43 
44 /*
45  * This gets called when the timer event triggers. We set the "expired"
46  * flag, but we do not re-arm the timer (in case it's necessary,
47  * tintv.tv64 != 0) until the timer is accessed.
48  */
49 static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
50 {
51 	struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
52 	unsigned long flags;
53 
54 	spin_lock_irqsave(&ctx->wqh.lock, flags);
55 	ctx->expired = 1;
56 	ctx->ticks++;
57 	wake_up_locked(&ctx->wqh);
58 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
59 
60 	return HRTIMER_NORESTART;
61 }
62 
63 /*
64  * Called when the clock was set to cancel the timers in the cancel
65  * list. This will wake up processes waiting on these timers. The
66  * wake-up requires ctx->ticks to be non zero, therefore we increment
67  * it before calling wake_up_locked().
68  */
69 void timerfd_clock_was_set(void)
70 {
71 	ktime_t moffs = ktime_get_monotonic_offset();
72 	struct timerfd_ctx *ctx;
73 	unsigned long flags;
74 
75 	rcu_read_lock();
76 	list_for_each_entry_rcu(ctx, &cancel_list, clist) {
77 		if (!ctx->might_cancel)
78 			continue;
79 		spin_lock_irqsave(&ctx->wqh.lock, flags);
80 		if (ctx->moffs.tv64 != moffs.tv64) {
81 			ctx->moffs.tv64 = KTIME_MAX;
82 			ctx->ticks++;
83 			wake_up_locked(&ctx->wqh);
84 		}
85 		spin_unlock_irqrestore(&ctx->wqh.lock, flags);
86 	}
87 	rcu_read_unlock();
88 }
89 
90 static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
91 {
92 	if (ctx->might_cancel) {
93 		ctx->might_cancel = false;
94 		spin_lock(&cancel_lock);
95 		list_del_rcu(&ctx->clist);
96 		spin_unlock(&cancel_lock);
97 	}
98 }
99 
100 static bool timerfd_canceled(struct timerfd_ctx *ctx)
101 {
102 	if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
103 		return false;
104 	ctx->moffs = ktime_get_monotonic_offset();
105 	return true;
106 }
107 
108 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
109 {
110 	if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
111 	    (flags & TFD_TIMER_CANCEL_ON_SET)) {
112 		if (!ctx->might_cancel) {
113 			ctx->might_cancel = true;
114 			spin_lock(&cancel_lock);
115 			list_add_rcu(&ctx->clist, &cancel_list);
116 			spin_unlock(&cancel_lock);
117 		}
118 	} else if (ctx->might_cancel) {
119 		timerfd_remove_cancel(ctx);
120 	}
121 }
122 
123 static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
124 {
125 	ktime_t remaining;
126 
127 	remaining = hrtimer_expires_remaining(&ctx->tmr);
128 	return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
129 }
130 
131 static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
132 			 const struct itimerspec *ktmr)
133 {
134 	enum hrtimer_mode htmode;
135 	ktime_t texp;
136 	int clockid = ctx->clockid;
137 
138 	htmode = (flags & TFD_TIMER_ABSTIME) ?
139 		HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
140 
141 	texp = timespec_to_ktime(ktmr->it_value);
142 	ctx->expired = 0;
143 	ctx->ticks = 0;
144 	ctx->tintv = timespec_to_ktime(ktmr->it_interval);
145 	hrtimer_init(&ctx->tmr, clockid, htmode);
146 	hrtimer_set_expires(&ctx->tmr, texp);
147 	ctx->tmr.function = timerfd_tmrproc;
148 	if (texp.tv64 != 0) {
149 		hrtimer_start(&ctx->tmr, texp, htmode);
150 		if (timerfd_canceled(ctx))
151 			return -ECANCELED;
152 	}
153 	return 0;
154 }
155 
156 static int timerfd_release(struct inode *inode, struct file *file)
157 {
158 	struct timerfd_ctx *ctx = file->private_data;
159 
160 	timerfd_remove_cancel(ctx);
161 	hrtimer_cancel(&ctx->tmr);
162 	kfree_rcu(ctx, rcu);
163 	return 0;
164 }
165 
166 static unsigned int timerfd_poll(struct file *file, poll_table *wait)
167 {
168 	struct timerfd_ctx *ctx = file->private_data;
169 	unsigned int events = 0;
170 	unsigned long flags;
171 
172 	poll_wait(file, &ctx->wqh, wait);
173 
174 	spin_lock_irqsave(&ctx->wqh.lock, flags);
175 	if (ctx->ticks)
176 		events |= POLLIN;
177 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
178 
179 	return events;
180 }
181 
182 static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
183 			    loff_t *ppos)
184 {
185 	struct timerfd_ctx *ctx = file->private_data;
186 	ssize_t res;
187 	u64 ticks = 0;
188 
189 	if (count < sizeof(ticks))
190 		return -EINVAL;
191 	spin_lock_irq(&ctx->wqh.lock);
192 	if (file->f_flags & O_NONBLOCK)
193 		res = -EAGAIN;
194 	else
195 		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
196 
197 	/*
198 	 * If clock has changed, we do not care about the
199 	 * ticks and we do not rearm the timer. Userspace must
200 	 * reevaluate anyway.
201 	 */
202 	if (timerfd_canceled(ctx)) {
203 		ctx->ticks = 0;
204 		ctx->expired = 0;
205 		res = -ECANCELED;
206 	}
207 
208 	if (ctx->ticks) {
209 		ticks = ctx->ticks;
210 
211 		if (ctx->expired && ctx->tintv.tv64) {
212 			/*
213 			 * If tintv.tv64 != 0, this is a periodic timer that
214 			 * needs to be re-armed. We avoid doing it in the timer
215 			 * callback to avoid DoS attacks specifying a very
216 			 * short timer period.
217 			 */
218 			ticks += hrtimer_forward_now(&ctx->tmr,
219 						     ctx->tintv) - 1;
220 			hrtimer_restart(&ctx->tmr);
221 		}
222 		ctx->expired = 0;
223 		ctx->ticks = 0;
224 	}
225 	spin_unlock_irq(&ctx->wqh.lock);
226 	if (ticks)
227 		res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
228 	return res;
229 }
230 
231 static const struct file_operations timerfd_fops = {
232 	.release	= timerfd_release,
233 	.poll		= timerfd_poll,
234 	.read		= timerfd_read,
235 	.llseek		= noop_llseek,
236 };
237 
238 static int timerfd_fget(int fd, struct fd *p)
239 {
240 	struct fd f = fdget(fd);
241 	if (!f.file)
242 		return -EBADF;
243 	if (f.file->f_op != &timerfd_fops) {
244 		fdput(f);
245 		return -EINVAL;
246 	}
247 	*p = f;
248 	return 0;
249 }
250 
251 SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
252 {
253 	int ufd;
254 	struct timerfd_ctx *ctx;
255 
256 	/* Check the TFD_* constants for consistency.  */
257 	BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
258 	BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
259 
260 	if ((flags & ~TFD_CREATE_FLAGS) ||
261 	    (clockid != CLOCK_MONOTONIC &&
262 	     clockid != CLOCK_REALTIME))
263 		return -EINVAL;
264 
265 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
266 	if (!ctx)
267 		return -ENOMEM;
268 
269 	init_waitqueue_head(&ctx->wqh);
270 	ctx->clockid = clockid;
271 	hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
272 	ctx->moffs = ktime_get_monotonic_offset();
273 
274 	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
275 			       O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
276 	if (ufd < 0)
277 		kfree(ctx);
278 
279 	return ufd;
280 }
281 
282 static int do_timerfd_settime(int ufd, int flags,
283 		const struct itimerspec *new,
284 		struct itimerspec *old)
285 {
286 	struct fd f;
287 	struct timerfd_ctx *ctx;
288 	int ret;
289 
290 	if ((flags & ~TFD_SETTIME_FLAGS) ||
291 	    !timespec_valid(&new->it_value) ||
292 	    !timespec_valid(&new->it_interval))
293 		return -EINVAL;
294 
295 	ret = timerfd_fget(ufd, &f);
296 	if (ret)
297 		return ret;
298 	ctx = f.file->private_data;
299 
300 	timerfd_setup_cancel(ctx, flags);
301 
302 	/*
303 	 * We need to stop the existing timer before reprogramming
304 	 * it to the new values.
305 	 */
306 	for (;;) {
307 		spin_lock_irq(&ctx->wqh.lock);
308 		if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
309 			break;
310 		spin_unlock_irq(&ctx->wqh.lock);
311 		cpu_relax();
312 	}
313 
314 	/*
315 	 * If the timer is expired and it's periodic, we need to advance it
316 	 * because the caller may want to know the previous expiration time.
317 	 * We do not update "ticks" and "expired" since the timer will be
318 	 * re-programmed again in the following timerfd_setup() call.
319 	 */
320 	if (ctx->expired && ctx->tintv.tv64)
321 		hrtimer_forward_now(&ctx->tmr, ctx->tintv);
322 
323 	old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
324 	old->it_interval = ktime_to_timespec(ctx->tintv);
325 
326 	/*
327 	 * Re-program the timer to the new value ...
328 	 */
329 	ret = timerfd_setup(ctx, flags, new);
330 
331 	spin_unlock_irq(&ctx->wqh.lock);
332 	fdput(f);
333 	return ret;
334 }
335 
336 static int do_timerfd_gettime(int ufd, struct itimerspec *t)
337 {
338 	struct fd f;
339 	struct timerfd_ctx *ctx;
340 	int ret = timerfd_fget(ufd, &f);
341 	if (ret)
342 		return ret;
343 	ctx = f.file->private_data;
344 
345 	spin_lock_irq(&ctx->wqh.lock);
346 	if (ctx->expired && ctx->tintv.tv64) {
347 		ctx->expired = 0;
348 		ctx->ticks +=
349 			hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
350 		hrtimer_restart(&ctx->tmr);
351 	}
352 	t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
353 	t->it_interval = ktime_to_timespec(ctx->tintv);
354 	spin_unlock_irq(&ctx->wqh.lock);
355 	fdput(f);
356 	return 0;
357 }
358 
359 SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
360 		const struct itimerspec __user *, utmr,
361 		struct itimerspec __user *, otmr)
362 {
363 	struct itimerspec new, old;
364 	int ret;
365 
366 	if (copy_from_user(&new, utmr, sizeof(new)))
367 		return -EFAULT;
368 	ret = do_timerfd_settime(ufd, flags, &new, &old);
369 	if (ret)
370 		return ret;
371 	if (otmr && copy_to_user(otmr, &old, sizeof(old)))
372 		return -EFAULT;
373 
374 	return ret;
375 }
376 
377 SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
378 {
379 	struct itimerspec kotmr;
380 	int ret = do_timerfd_gettime(ufd, &kotmr);
381 	if (ret)
382 		return ret;
383 	return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
384 }
385 
386 #ifdef CONFIG_COMPAT
387 COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
388 		const struct compat_itimerspec __user *, utmr,
389 		struct compat_itimerspec __user *, otmr)
390 {
391 	struct itimerspec new, old;
392 	int ret;
393 
394 	if (get_compat_itimerspec(&new, utmr))
395 		return -EFAULT;
396 	ret = do_timerfd_settime(ufd, flags, &new, &old);
397 	if (ret)
398 		return ret;
399 	if (otmr && put_compat_itimerspec(otmr, &old))
400 		return -EFAULT;
401 	return ret;
402 }
403 
404 COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
405 		struct compat_itimerspec __user *, otmr)
406 {
407 	struct itimerspec kotmr;
408 	int ret = do_timerfd_gettime(ufd, &kotmr);
409 	if (ret)
410 		return ret;
411 	return put_compat_itimerspec(otmr, &kotmr) ? -EFAULT: 0;
412 }
413 #endif
414