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