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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * fs/eventfd.c
4 *
5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 *
7 */
8
9#include <linux/file.h>
10#include <linux/poll.h>
11#include <linux/init.h>
12#include <linux/fs.h>
13#include <linux/sched/signal.h>
14#include <linux/kernel.h>
15#include <linux/slab.h>
16#include <linux/list.h>
17#include <linux/spinlock.h>
18#include <linux/anon_inodes.h>
19#include <linux/syscalls.h>
20#include <linux/export.h>
21#include <linux/kref.h>
22#include <linux/eventfd.h>
23#include <linux/proc_fs.h>
24#include <linux/seq_file.h>
25#include <linux/idr.h>
26#include <linux/uio.h>
27
28static DEFINE_IDA(eventfd_ida);
29
30struct eventfd_ctx {
31 struct kref kref;
32 wait_queue_head_t wqh;
33 /*
34 * Every time that a write(2) is performed on an eventfd, the
35 * value of the __u64 being written is added to "count" and a
36 * wakeup is performed on "wqh". If EFD_SEMAPHORE flag was not
37 * specified, a read(2) will return the "count" value to userspace,
38 * and will reset "count" to zero. The kernel side eventfd_signal()
39 * also, adds to the "count" counter and issue a wakeup.
40 */
41 __u64 count;
42 unsigned int flags;
43 int id;
44};
45
46/**
47 * eventfd_signal_mask - Increment the event counter
48 * @ctx: [in] Pointer to the eventfd context.
49 * @mask: [in] poll mask
50 *
51 * This function is supposed to be called by the kernel in paths that do not
52 * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
53 * value, and we signal this as overflow condition by returning a EPOLLERR
54 * to poll(2).
55 */
56void eventfd_signal_mask(struct eventfd_ctx *ctx, __poll_t mask)
57{
58 unsigned long flags;
59
60 /*
61 * Deadlock or stack overflow issues can happen if we recurse here
62 * through waitqueue wakeup handlers. If the caller users potentially
63 * nested waitqueues with custom wakeup handlers, then it should
64 * check eventfd_signal_allowed() before calling this function. If
65 * it returns false, the eventfd_signal() call should be deferred to a
66 * safe context.
67 */
68 if (WARN_ON_ONCE(current->in_eventfd))
69 return;
70
71 spin_lock_irqsave(&ctx->wqh.lock, flags);
72 current->in_eventfd = 1;
73 if (ctx->count < ULLONG_MAX)
74 ctx->count++;
75 if (waitqueue_active(&ctx->wqh))
76 wake_up_locked_poll(&ctx->wqh, EPOLLIN | mask);
77 current->in_eventfd = 0;
78 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
79}
80EXPORT_SYMBOL_GPL(eventfd_signal_mask);
81
82static void eventfd_free_ctx(struct eventfd_ctx *ctx)
83{
84 if (ctx->id >= 0)
85 ida_free(&eventfd_ida, ctx->id);
86 kfree(ctx);
87}
88
89static void eventfd_free(struct kref *kref)
90{
91 struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
92
93 eventfd_free_ctx(ctx);
94}
95
96/**
97 * eventfd_ctx_put - Releases a reference to the internal eventfd context.
98 * @ctx: [in] Pointer to eventfd context.
99 *
100 * The eventfd context reference must have been previously acquired either
101 * with eventfd_ctx_fdget() or eventfd_ctx_fileget().
102 */
103void eventfd_ctx_put(struct eventfd_ctx *ctx)
104{
105 kref_put(&ctx->kref, eventfd_free);
106}
107EXPORT_SYMBOL_GPL(eventfd_ctx_put);
108
109static int eventfd_release(struct inode *inode, struct file *file)
110{
111 struct eventfd_ctx *ctx = file->private_data;
112
113 wake_up_poll(&ctx->wqh, EPOLLHUP);
114 eventfd_ctx_put(ctx);
115 return 0;
116}
117
118static __poll_t eventfd_poll(struct file *file, poll_table *wait)
119{
120 struct eventfd_ctx *ctx = file->private_data;
121 __poll_t events = 0;
122 u64 count;
123
124 poll_wait(file, &ctx->wqh, wait);
125
126 /*
127 * All writes to ctx->count occur within ctx->wqh.lock. This read
128 * can be done outside ctx->wqh.lock because we know that poll_wait
129 * takes that lock (through add_wait_queue) if our caller will sleep.
130 *
131 * The read _can_ therefore seep into add_wait_queue's critical
132 * section, but cannot move above it! add_wait_queue's spin_lock acts
133 * as an acquire barrier and ensures that the read be ordered properly
134 * against the writes. The following CAN happen and is safe:
135 *
136 * poll write
137 * ----------------- ------------
138 * lock ctx->wqh.lock (in poll_wait)
139 * count = ctx->count
140 * __add_wait_queue
141 * unlock ctx->wqh.lock
142 * lock ctx->qwh.lock
143 * ctx->count += n
144 * if (waitqueue_active)
145 * wake_up_locked_poll
146 * unlock ctx->qwh.lock
147 * eventfd_poll returns 0
148 *
149 * but the following, which would miss a wakeup, cannot happen:
150 *
151 * poll write
152 * ----------------- ------------
153 * count = ctx->count (INVALID!)
154 * lock ctx->qwh.lock
155 * ctx->count += n
156 * **waitqueue_active is false**
157 * **no wake_up_locked_poll!**
158 * unlock ctx->qwh.lock
159 * lock ctx->wqh.lock (in poll_wait)
160 * __add_wait_queue
161 * unlock ctx->wqh.lock
162 * eventfd_poll returns 0
163 */
164 count = READ_ONCE(ctx->count);
165
166 if (count > 0)
167 events |= EPOLLIN;
168 if (count == ULLONG_MAX)
169 events |= EPOLLERR;
170 if (ULLONG_MAX - 1 > count)
171 events |= EPOLLOUT;
172
173 return events;
174}
175
176void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
177{
178 lockdep_assert_held(&ctx->wqh.lock);
179
180 *cnt = ((ctx->flags & EFD_SEMAPHORE) && ctx->count) ? 1 : ctx->count;
181 ctx->count -= *cnt;
182}
183EXPORT_SYMBOL_GPL(eventfd_ctx_do_read);
184
185/**
186 * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
187 * @ctx: [in] Pointer to eventfd context.
188 * @wait: [in] Wait queue to be removed.
189 * @cnt: [out] Pointer to the 64-bit counter value.
190 *
191 * Returns %0 if successful, or the following error codes:
192 *
193 * -EAGAIN : The operation would have blocked.
194 *
195 * This is used to atomically remove a wait queue entry from the eventfd wait
196 * queue head, and read/reset the counter value.
197 */
198int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait,
199 __u64 *cnt)
200{
201 unsigned long flags;
202
203 spin_lock_irqsave(&ctx->wqh.lock, flags);
204 eventfd_ctx_do_read(ctx, cnt);
205 __remove_wait_queue(&ctx->wqh, wait);
206 if (*cnt != 0 && waitqueue_active(&ctx->wqh))
207 wake_up_locked_poll(&ctx->wqh, EPOLLOUT);
208 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
209
210 return *cnt != 0 ? 0 : -EAGAIN;
211}
212EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
213
214static ssize_t eventfd_read(struct kiocb *iocb, struct iov_iter *to)
215{
216 struct file *file = iocb->ki_filp;
217 struct eventfd_ctx *ctx = file->private_data;
218 __u64 ucnt = 0;
219
220 if (iov_iter_count(to) < sizeof(ucnt))
221 return -EINVAL;
222 spin_lock_irq(&ctx->wqh.lock);
223 if (!ctx->count) {
224 if ((file->f_flags & O_NONBLOCK) ||
225 (iocb->ki_flags & IOCB_NOWAIT)) {
226 spin_unlock_irq(&ctx->wqh.lock);
227 return -EAGAIN;
228 }
229
230 if (wait_event_interruptible_locked_irq(ctx->wqh, ctx->count)) {
231 spin_unlock_irq(&ctx->wqh.lock);
232 return -ERESTARTSYS;
233 }
234 }
235 eventfd_ctx_do_read(ctx, &ucnt);
236 current->in_eventfd = 1;
237 if (waitqueue_active(&ctx->wqh))
238 wake_up_locked_poll(&ctx->wqh, EPOLLOUT);
239 current->in_eventfd = 0;
240 spin_unlock_irq(&ctx->wqh.lock);
241 if (unlikely(copy_to_iter(&ucnt, sizeof(ucnt), to) != sizeof(ucnt)))
242 return -EFAULT;
243
244 return sizeof(ucnt);
245}
246
247static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
248 loff_t *ppos)
249{
250 struct eventfd_ctx *ctx = file->private_data;
251 ssize_t res;
252 __u64 ucnt;
253
254 if (count != sizeof(ucnt))
255 return -EINVAL;
256 if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
257 return -EFAULT;
258 if (ucnt == ULLONG_MAX)
259 return -EINVAL;
260 spin_lock_irq(&ctx->wqh.lock);
261 res = -EAGAIN;
262 if (ULLONG_MAX - ctx->count > ucnt)
263 res = sizeof(ucnt);
264 else if (!(file->f_flags & O_NONBLOCK)) {
265 res = wait_event_interruptible_locked_irq(ctx->wqh,
266 ULLONG_MAX - ctx->count > ucnt);
267 if (!res)
268 res = sizeof(ucnt);
269 }
270 if (likely(res > 0)) {
271 ctx->count += ucnt;
272 current->in_eventfd = 1;
273 if (waitqueue_active(&ctx->wqh))
274 wake_up_locked_poll(&ctx->wqh, EPOLLIN);
275 current->in_eventfd = 0;
276 }
277 spin_unlock_irq(&ctx->wqh.lock);
278
279 return res;
280}
281
282#ifdef CONFIG_PROC_FS
283static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
284{
285 struct eventfd_ctx *ctx = f->private_data;
286 __u64 cnt;
287
288 spin_lock_irq(&ctx->wqh.lock);
289 cnt = ctx->count;
290 spin_unlock_irq(&ctx->wqh.lock);
291
292 seq_printf(m,
293 "eventfd-count: %16llx\n"
294 "eventfd-id: %d\n"
295 "eventfd-semaphore: %d\n",
296 cnt,
297 ctx->id,
298 !!(ctx->flags & EFD_SEMAPHORE));
299}
300#endif
301
302static const struct file_operations eventfd_fops = {
303#ifdef CONFIG_PROC_FS
304 .show_fdinfo = eventfd_show_fdinfo,
305#endif
306 .release = eventfd_release,
307 .poll = eventfd_poll,
308 .read_iter = eventfd_read,
309 .write = eventfd_write,
310 .llseek = noop_llseek,
311};
312
313/**
314 * eventfd_fget - Acquire a reference of an eventfd file descriptor.
315 * @fd: [in] Eventfd file descriptor.
316 *
317 * Returns a pointer to the eventfd file structure in case of success, or the
318 * following error pointer:
319 *
320 * -EBADF : Invalid @fd file descriptor.
321 * -EINVAL : The @fd file descriptor is not an eventfd file.
322 */
323struct file *eventfd_fget(int fd)
324{
325 struct file *file;
326
327 file = fget(fd);
328 if (!file)
329 return ERR_PTR(-EBADF);
330 if (file->f_op != &eventfd_fops) {
331 fput(file);
332 return ERR_PTR(-EINVAL);
333 }
334
335 return file;
336}
337EXPORT_SYMBOL_GPL(eventfd_fget);
338
339/**
340 * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
341 * @fd: [in] Eventfd file descriptor.
342 *
343 * Returns a pointer to the internal eventfd context, otherwise the error
344 * pointers returned by the following functions:
345 *
346 * eventfd_fget
347 */
348struct eventfd_ctx *eventfd_ctx_fdget(int fd)
349{
350 CLASS(fd, f)(fd);
351 if (fd_empty(f))
352 return ERR_PTR(-EBADF);
353 return eventfd_ctx_fileget(fd_file(f));
354}
355EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
356
357/**
358 * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
359 * @file: [in] Eventfd file pointer.
360 *
361 * Returns a pointer to the internal eventfd context, otherwise the error
362 * pointer:
363 *
364 * -EINVAL : The @fd file descriptor is not an eventfd file.
365 */
366struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
367{
368 struct eventfd_ctx *ctx;
369
370 if (file->f_op != &eventfd_fops)
371 return ERR_PTR(-EINVAL);
372
373 ctx = file->private_data;
374 kref_get(&ctx->kref);
375 return ctx;
376}
377EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
378
379static int do_eventfd(unsigned int count, int flags)
380{
381 struct eventfd_ctx *ctx;
382 struct file *file;
383 int fd;
384
385 /* Check the EFD_* constants for consistency. */
386 BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
387 BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
388 BUILD_BUG_ON(EFD_SEMAPHORE != (1 << 0));
389
390 if (flags & ~EFD_FLAGS_SET)
391 return -EINVAL;
392
393 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
394 if (!ctx)
395 return -ENOMEM;
396
397 kref_init(&ctx->kref);
398 init_waitqueue_head(&ctx->wqh);
399 ctx->count = count;
400 ctx->flags = flags;
401 ctx->id = ida_alloc(&eventfd_ida, GFP_KERNEL);
402
403 flags &= EFD_SHARED_FCNTL_FLAGS;
404 flags |= O_RDWR;
405 fd = get_unused_fd_flags(flags);
406 if (fd < 0)
407 goto err;
408
409 file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, flags);
410 if (IS_ERR(file)) {
411 put_unused_fd(fd);
412 fd = PTR_ERR(file);
413 goto err;
414 }
415
416 file->f_mode |= FMODE_NOWAIT;
417 fd_install(fd, file);
418 return fd;
419err:
420 eventfd_free_ctx(ctx);
421 return fd;
422}
423
424SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
425{
426 return do_eventfd(count, flags);
427}
428
429SYSCALL_DEFINE1(eventfd, unsigned int, count)
430{
431 return do_eventfd(count, 0);
432}
433
1/*
2 * fs/eventfd.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 *
6 */
7
8#include <linux/file.h>
9#include <linux/poll.h>
10#include <linux/init.h>
11#include <linux/fs.h>
12#include <linux/sched.h>
13#include <linux/kernel.h>
14#include <linux/slab.h>
15#include <linux/list.h>
16#include <linux/spinlock.h>
17#include <linux/anon_inodes.h>
18#include <linux/syscalls.h>
19#include <linux/export.h>
20#include <linux/kref.h>
21#include <linux/eventfd.h>
22#include <linux/proc_fs.h>
23#include <linux/seq_file.h>
24
25struct eventfd_ctx {
26 struct kref kref;
27 wait_queue_head_t wqh;
28 /*
29 * Every time that a write(2) is performed on an eventfd, the
30 * value of the __u64 being written is added to "count" and a
31 * wakeup is performed on "wqh". A read(2) will return the "count"
32 * value to userspace, and will reset "count" to zero. The kernel
33 * side eventfd_signal() also, adds to the "count" counter and
34 * issue a wakeup.
35 */
36 __u64 count;
37 unsigned int flags;
38};
39
40/**
41 * eventfd_signal - Adds @n to the eventfd counter.
42 * @ctx: [in] Pointer to the eventfd context.
43 * @n: [in] Value of the counter to be added to the eventfd internal counter.
44 * The value cannot be negative.
45 *
46 * This function is supposed to be called by the kernel in paths that do not
47 * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX
48 * value, and we signal this as overflow condition by returning a POLLERR
49 * to poll(2).
50 *
51 * Returns the amount by which the counter was incremented. This will be less
52 * than @n if the counter has overflowed.
53 */
54__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
55{
56 unsigned long flags;
57
58 spin_lock_irqsave(&ctx->wqh.lock, flags);
59 if (ULLONG_MAX - ctx->count < n)
60 n = ULLONG_MAX - ctx->count;
61 ctx->count += n;
62 if (waitqueue_active(&ctx->wqh))
63 wake_up_locked_poll(&ctx->wqh, POLLIN);
64 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
65
66 return n;
67}
68EXPORT_SYMBOL_GPL(eventfd_signal);
69
70static void eventfd_free_ctx(struct eventfd_ctx *ctx)
71{
72 kfree(ctx);
73}
74
75static void eventfd_free(struct kref *kref)
76{
77 struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
78
79 eventfd_free_ctx(ctx);
80}
81
82/**
83 * eventfd_ctx_get - Acquires a reference to the internal eventfd context.
84 * @ctx: [in] Pointer to the eventfd context.
85 *
86 * Returns: In case of success, returns a pointer to the eventfd context.
87 */
88struct eventfd_ctx *eventfd_ctx_get(struct eventfd_ctx *ctx)
89{
90 kref_get(&ctx->kref);
91 return ctx;
92}
93EXPORT_SYMBOL_GPL(eventfd_ctx_get);
94
95/**
96 * eventfd_ctx_put - Releases a reference to the internal eventfd context.
97 * @ctx: [in] Pointer to eventfd context.
98 *
99 * The eventfd context reference must have been previously acquired either
100 * with eventfd_ctx_get() or eventfd_ctx_fdget().
101 */
102void eventfd_ctx_put(struct eventfd_ctx *ctx)
103{
104 kref_put(&ctx->kref, eventfd_free);
105}
106EXPORT_SYMBOL_GPL(eventfd_ctx_put);
107
108static int eventfd_release(struct inode *inode, struct file *file)
109{
110 struct eventfd_ctx *ctx = file->private_data;
111
112 wake_up_poll(&ctx->wqh, POLLHUP);
113 eventfd_ctx_put(ctx);
114 return 0;
115}
116
117static unsigned int eventfd_poll(struct file *file, poll_table *wait)
118{
119 struct eventfd_ctx *ctx = file->private_data;
120 unsigned int events = 0;
121 u64 count;
122
123 poll_wait(file, &ctx->wqh, wait);
124
125 /*
126 * All writes to ctx->count occur within ctx->wqh.lock. This read
127 * can be done outside ctx->wqh.lock because we know that poll_wait
128 * takes that lock (through add_wait_queue) if our caller will sleep.
129 *
130 * The read _can_ therefore seep into add_wait_queue's critical
131 * section, but cannot move above it! add_wait_queue's spin_lock acts
132 * as an acquire barrier and ensures that the read be ordered properly
133 * against the writes. The following CAN happen and is safe:
134 *
135 * poll write
136 * ----------------- ------------
137 * lock ctx->wqh.lock (in poll_wait)
138 * count = ctx->count
139 * __add_wait_queue
140 * unlock ctx->wqh.lock
141 * lock ctx->qwh.lock
142 * ctx->count += n
143 * if (waitqueue_active)
144 * wake_up_locked_poll
145 * unlock ctx->qwh.lock
146 * eventfd_poll returns 0
147 *
148 * but the following, which would miss a wakeup, cannot happen:
149 *
150 * poll write
151 * ----------------- ------------
152 * count = ctx->count (INVALID!)
153 * lock ctx->qwh.lock
154 * ctx->count += n
155 * **waitqueue_active is false**
156 * **no wake_up_locked_poll!**
157 * unlock ctx->qwh.lock
158 * lock ctx->wqh.lock (in poll_wait)
159 * __add_wait_queue
160 * unlock ctx->wqh.lock
161 * eventfd_poll returns 0
162 */
163 count = READ_ONCE(ctx->count);
164
165 if (count > 0)
166 events |= POLLIN;
167 if (count == ULLONG_MAX)
168 events |= POLLERR;
169 if (ULLONG_MAX - 1 > count)
170 events |= POLLOUT;
171
172 return events;
173}
174
175static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
176{
177 *cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
178 ctx->count -= *cnt;
179}
180
181/**
182 * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
183 * @ctx: [in] Pointer to eventfd context.
184 * @wait: [in] Wait queue to be removed.
185 * @cnt: [out] Pointer to the 64-bit counter value.
186 *
187 * Returns %0 if successful, or the following error codes:
188 *
189 * -EAGAIN : The operation would have blocked.
190 *
191 * This is used to atomically remove a wait queue entry from the eventfd wait
192 * queue head, and read/reset the counter value.
193 */
194int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
195 __u64 *cnt)
196{
197 unsigned long flags;
198
199 spin_lock_irqsave(&ctx->wqh.lock, flags);
200 eventfd_ctx_do_read(ctx, cnt);
201 __remove_wait_queue(&ctx->wqh, wait);
202 if (*cnt != 0 && waitqueue_active(&ctx->wqh))
203 wake_up_locked_poll(&ctx->wqh, POLLOUT);
204 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
205
206 return *cnt != 0 ? 0 : -EAGAIN;
207}
208EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
209
210/**
211 * eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
212 * @ctx: [in] Pointer to eventfd context.
213 * @no_wait: [in] Different from zero if the operation should not block.
214 * @cnt: [out] Pointer to the 64-bit counter value.
215 *
216 * Returns %0 if successful, or the following error codes:
217 *
218 * -EAGAIN : The operation would have blocked but @no_wait was non-zero.
219 * -ERESTARTSYS : A signal interrupted the wait operation.
220 *
221 * If @no_wait is zero, the function might sleep until the eventfd internal
222 * counter becomes greater than zero.
223 */
224ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
225{
226 ssize_t res;
227 DECLARE_WAITQUEUE(wait, current);
228
229 spin_lock_irq(&ctx->wqh.lock);
230 *cnt = 0;
231 res = -EAGAIN;
232 if (ctx->count > 0)
233 res = 0;
234 else if (!no_wait) {
235 __add_wait_queue(&ctx->wqh, &wait);
236 for (;;) {
237 set_current_state(TASK_INTERRUPTIBLE);
238 if (ctx->count > 0) {
239 res = 0;
240 break;
241 }
242 if (signal_pending(current)) {
243 res = -ERESTARTSYS;
244 break;
245 }
246 spin_unlock_irq(&ctx->wqh.lock);
247 schedule();
248 spin_lock_irq(&ctx->wqh.lock);
249 }
250 __remove_wait_queue(&ctx->wqh, &wait);
251 __set_current_state(TASK_RUNNING);
252 }
253 if (likely(res == 0)) {
254 eventfd_ctx_do_read(ctx, cnt);
255 if (waitqueue_active(&ctx->wqh))
256 wake_up_locked_poll(&ctx->wqh, POLLOUT);
257 }
258 spin_unlock_irq(&ctx->wqh.lock);
259
260 return res;
261}
262EXPORT_SYMBOL_GPL(eventfd_ctx_read);
263
264static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
265 loff_t *ppos)
266{
267 struct eventfd_ctx *ctx = file->private_data;
268 ssize_t res;
269 __u64 cnt;
270
271 if (count < sizeof(cnt))
272 return -EINVAL;
273 res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
274 if (res < 0)
275 return res;
276
277 return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
278}
279
280static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
281 loff_t *ppos)
282{
283 struct eventfd_ctx *ctx = file->private_data;
284 ssize_t res;
285 __u64 ucnt;
286 DECLARE_WAITQUEUE(wait, current);
287
288 if (count < sizeof(ucnt))
289 return -EINVAL;
290 if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
291 return -EFAULT;
292 if (ucnt == ULLONG_MAX)
293 return -EINVAL;
294 spin_lock_irq(&ctx->wqh.lock);
295 res = -EAGAIN;
296 if (ULLONG_MAX - ctx->count > ucnt)
297 res = sizeof(ucnt);
298 else if (!(file->f_flags & O_NONBLOCK)) {
299 __add_wait_queue(&ctx->wqh, &wait);
300 for (res = 0;;) {
301 set_current_state(TASK_INTERRUPTIBLE);
302 if (ULLONG_MAX - ctx->count > ucnt) {
303 res = sizeof(ucnt);
304 break;
305 }
306 if (signal_pending(current)) {
307 res = -ERESTARTSYS;
308 break;
309 }
310 spin_unlock_irq(&ctx->wqh.lock);
311 schedule();
312 spin_lock_irq(&ctx->wqh.lock);
313 }
314 __remove_wait_queue(&ctx->wqh, &wait);
315 __set_current_state(TASK_RUNNING);
316 }
317 if (likely(res > 0)) {
318 ctx->count += ucnt;
319 if (waitqueue_active(&ctx->wqh))
320 wake_up_locked_poll(&ctx->wqh, POLLIN);
321 }
322 spin_unlock_irq(&ctx->wqh.lock);
323
324 return res;
325}
326
327#ifdef CONFIG_PROC_FS
328static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
329{
330 struct eventfd_ctx *ctx = f->private_data;
331
332 spin_lock_irq(&ctx->wqh.lock);
333 seq_printf(m, "eventfd-count: %16llx\n",
334 (unsigned long long)ctx->count);
335 spin_unlock_irq(&ctx->wqh.lock);
336}
337#endif
338
339static const struct file_operations eventfd_fops = {
340#ifdef CONFIG_PROC_FS
341 .show_fdinfo = eventfd_show_fdinfo,
342#endif
343 .release = eventfd_release,
344 .poll = eventfd_poll,
345 .read = eventfd_read,
346 .write = eventfd_write,
347 .llseek = noop_llseek,
348};
349
350/**
351 * eventfd_fget - Acquire a reference of an eventfd file descriptor.
352 * @fd: [in] Eventfd file descriptor.
353 *
354 * Returns a pointer to the eventfd file structure in case of success, or the
355 * following error pointer:
356 *
357 * -EBADF : Invalid @fd file descriptor.
358 * -EINVAL : The @fd file descriptor is not an eventfd file.
359 */
360struct file *eventfd_fget(int fd)
361{
362 struct file *file;
363
364 file = fget(fd);
365 if (!file)
366 return ERR_PTR(-EBADF);
367 if (file->f_op != &eventfd_fops) {
368 fput(file);
369 return ERR_PTR(-EINVAL);
370 }
371
372 return file;
373}
374EXPORT_SYMBOL_GPL(eventfd_fget);
375
376/**
377 * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
378 * @fd: [in] Eventfd file descriptor.
379 *
380 * Returns a pointer to the internal eventfd context, otherwise the error
381 * pointers returned by the following functions:
382 *
383 * eventfd_fget
384 */
385struct eventfd_ctx *eventfd_ctx_fdget(int fd)
386{
387 struct eventfd_ctx *ctx;
388 struct fd f = fdget(fd);
389 if (!f.file)
390 return ERR_PTR(-EBADF);
391 ctx = eventfd_ctx_fileget(f.file);
392 fdput(f);
393 return ctx;
394}
395EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
396
397/**
398 * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
399 * @file: [in] Eventfd file pointer.
400 *
401 * Returns a pointer to the internal eventfd context, otherwise the error
402 * pointer:
403 *
404 * -EINVAL : The @fd file descriptor is not an eventfd file.
405 */
406struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
407{
408 if (file->f_op != &eventfd_fops)
409 return ERR_PTR(-EINVAL);
410
411 return eventfd_ctx_get(file->private_data);
412}
413EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
414
415/**
416 * eventfd_file_create - Creates an eventfd file pointer.
417 * @count: Initial eventfd counter value.
418 * @flags: Flags for the eventfd file.
419 *
420 * This function creates an eventfd file pointer, w/out installing it into
421 * the fd table. This is useful when the eventfd file is used during the
422 * initialization of data structures that require extra setup after the eventfd
423 * creation. So the eventfd creation is split into the file pointer creation
424 * phase, and the file descriptor installation phase.
425 * In this way races with userspace closing the newly installed file descriptor
426 * can be avoided.
427 * Returns an eventfd file pointer, or a proper error pointer.
428 */
429struct file *eventfd_file_create(unsigned int count, int flags)
430{
431 struct file *file;
432 struct eventfd_ctx *ctx;
433
434 /* Check the EFD_* constants for consistency. */
435 BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
436 BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
437
438 if (flags & ~EFD_FLAGS_SET)
439 return ERR_PTR(-EINVAL);
440
441 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
442 if (!ctx)
443 return ERR_PTR(-ENOMEM);
444
445 kref_init(&ctx->kref);
446 init_waitqueue_head(&ctx->wqh);
447 ctx->count = count;
448 ctx->flags = flags;
449
450 file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx,
451 O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
452 if (IS_ERR(file))
453 eventfd_free_ctx(ctx);
454
455 return file;
456}
457
458SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
459{
460 int fd, error;
461 struct file *file;
462
463 error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS);
464 if (error < 0)
465 return error;
466 fd = error;
467
468 file = eventfd_file_create(count, flags);
469 if (IS_ERR(file)) {
470 error = PTR_ERR(file);
471 goto err_put_unused_fd;
472 }
473 fd_install(fd, file);
474
475 return fd;
476
477err_put_unused_fd:
478 put_unused_fd(fd);
479
480 return error;
481}
482
483SYSCALL_DEFINE1(eventfd, unsigned int, count)
484{
485 return sys_eventfd2(count, 0);
486}
487