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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
27static DEFINE_IDA(eventfd_ida);
28
29struct eventfd_ctx {
30 struct kref kref;
31 wait_queue_head_t wqh;
32 /*
33 * Every time that a write(2) is performed on an eventfd, the
34 * value of the __u64 being written is added to "count" and a
35 * wakeup is performed on "wqh". A read(2) will return the "count"
36 * value to userspace, and will reset "count" to zero. The kernel
37 * side eventfd_signal() also, adds to the "count" counter and
38 * issue a wakeup.
39 */
40 __u64 count;
41 unsigned int flags;
42 int id;
43};
44
45/**
46 * eventfd_signal - Adds @n to the eventfd counter.
47 * @ctx: [in] Pointer to the eventfd context.
48 * @n: [in] Value of the counter to be added to the eventfd internal counter.
49 * The value cannot be negative.
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 *
56 * Returns the amount by which the counter was incremented. This will be less
57 * than @n if the counter has overflowed.
58 */
59__u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
60{
61 unsigned long flags;
62
63 spin_lock_irqsave(&ctx->wqh.lock, flags);
64 if (ULLONG_MAX - ctx->count < n)
65 n = ULLONG_MAX - ctx->count;
66 ctx->count += n;
67 if (waitqueue_active(&ctx->wqh))
68 wake_up_locked_poll(&ctx->wqh, EPOLLIN);
69 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
70
71 return n;
72}
73EXPORT_SYMBOL_GPL(eventfd_signal);
74
75static void eventfd_free_ctx(struct eventfd_ctx *ctx)
76{
77 if (ctx->id >= 0)
78 ida_simple_remove(&eventfd_ida, ctx->id);
79 kfree(ctx);
80}
81
82static void eventfd_free(struct kref *kref)
83{
84 struct eventfd_ctx *ctx = container_of(kref, struct eventfd_ctx, kref);
85
86 eventfd_free_ctx(ctx);
87}
88
89/**
90 * eventfd_ctx_put - Releases a reference to the internal eventfd context.
91 * @ctx: [in] Pointer to eventfd context.
92 *
93 * The eventfd context reference must have been previously acquired either
94 * with eventfd_ctx_fdget() or eventfd_ctx_fileget().
95 */
96void eventfd_ctx_put(struct eventfd_ctx *ctx)
97{
98 kref_put(&ctx->kref, eventfd_free);
99}
100EXPORT_SYMBOL_GPL(eventfd_ctx_put);
101
102static int eventfd_release(struct inode *inode, struct file *file)
103{
104 struct eventfd_ctx *ctx = file->private_data;
105
106 wake_up_poll(&ctx->wqh, EPOLLHUP);
107 eventfd_ctx_put(ctx);
108 return 0;
109}
110
111static __poll_t eventfd_poll(struct file *file, poll_table *wait)
112{
113 struct eventfd_ctx *ctx = file->private_data;
114 __poll_t events = 0;
115 u64 count;
116
117 poll_wait(file, &ctx->wqh, wait);
118
119 /*
120 * All writes to ctx->count occur within ctx->wqh.lock. This read
121 * can be done outside ctx->wqh.lock because we know that poll_wait
122 * takes that lock (through add_wait_queue) if our caller will sleep.
123 *
124 * The read _can_ therefore seep into add_wait_queue's critical
125 * section, but cannot move above it! add_wait_queue's spin_lock acts
126 * as an acquire barrier and ensures that the read be ordered properly
127 * against the writes. The following CAN happen and is safe:
128 *
129 * poll write
130 * ----------------- ------------
131 * lock ctx->wqh.lock (in poll_wait)
132 * count = ctx->count
133 * __add_wait_queue
134 * unlock ctx->wqh.lock
135 * lock ctx->qwh.lock
136 * ctx->count += n
137 * if (waitqueue_active)
138 * wake_up_locked_poll
139 * unlock ctx->qwh.lock
140 * eventfd_poll returns 0
141 *
142 * but the following, which would miss a wakeup, cannot happen:
143 *
144 * poll write
145 * ----------------- ------------
146 * count = ctx->count (INVALID!)
147 * lock ctx->qwh.lock
148 * ctx->count += n
149 * **waitqueue_active is false**
150 * **no wake_up_locked_poll!**
151 * unlock ctx->qwh.lock
152 * lock ctx->wqh.lock (in poll_wait)
153 * __add_wait_queue
154 * unlock ctx->wqh.lock
155 * eventfd_poll returns 0
156 */
157 count = READ_ONCE(ctx->count);
158
159 if (count > 0)
160 events |= EPOLLIN;
161 if (count == ULLONG_MAX)
162 events |= EPOLLERR;
163 if (ULLONG_MAX - 1 > count)
164 events |= EPOLLOUT;
165
166 return events;
167}
168
169static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
170{
171 *cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
172 ctx->count -= *cnt;
173}
174
175/**
176 * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
177 * @ctx: [in] Pointer to eventfd context.
178 * @wait: [in] Wait queue to be removed.
179 * @cnt: [out] Pointer to the 64-bit counter value.
180 *
181 * Returns %0 if successful, or the following error codes:
182 *
183 * -EAGAIN : The operation would have blocked.
184 *
185 * This is used to atomically remove a wait queue entry from the eventfd wait
186 * queue head, and read/reset the counter value.
187 */
188int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_entry_t *wait,
189 __u64 *cnt)
190{
191 unsigned long flags;
192
193 spin_lock_irqsave(&ctx->wqh.lock, flags);
194 eventfd_ctx_do_read(ctx, cnt);
195 __remove_wait_queue(&ctx->wqh, wait);
196 if (*cnt != 0 && waitqueue_active(&ctx->wqh))
197 wake_up_locked_poll(&ctx->wqh, EPOLLOUT);
198 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
199
200 return *cnt != 0 ? 0 : -EAGAIN;
201}
202EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
203
204static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
205 loff_t *ppos)
206{
207 struct eventfd_ctx *ctx = file->private_data;
208 ssize_t res;
209 __u64 ucnt = 0;
210 DECLARE_WAITQUEUE(wait, current);
211
212 if (count < sizeof(ucnt))
213 return -EINVAL;
214
215 spin_lock_irq(&ctx->wqh.lock);
216 res = -EAGAIN;
217 if (ctx->count > 0)
218 res = sizeof(ucnt);
219 else if (!(file->f_flags & O_NONBLOCK)) {
220 __add_wait_queue(&ctx->wqh, &wait);
221 for (;;) {
222 set_current_state(TASK_INTERRUPTIBLE);
223 if (ctx->count > 0) {
224 res = sizeof(ucnt);
225 break;
226 }
227 if (signal_pending(current)) {
228 res = -ERESTARTSYS;
229 break;
230 }
231 spin_unlock_irq(&ctx->wqh.lock);
232 schedule();
233 spin_lock_irq(&ctx->wqh.lock);
234 }
235 __remove_wait_queue(&ctx->wqh, &wait);
236 __set_current_state(TASK_RUNNING);
237 }
238 if (likely(res > 0)) {
239 eventfd_ctx_do_read(ctx, &ucnt);
240 if (waitqueue_active(&ctx->wqh))
241 wake_up_locked_poll(&ctx->wqh, EPOLLOUT);
242 }
243 spin_unlock_irq(&ctx->wqh.lock);
244
245 if (res > 0 && put_user(ucnt, (__u64 __user *)buf))
246 return -EFAULT;
247
248 return res;
249}
250
251static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
252 loff_t *ppos)
253{
254 struct eventfd_ctx *ctx = file->private_data;
255 ssize_t res;
256 __u64 ucnt;
257 DECLARE_WAITQUEUE(wait, current);
258
259 if (count < sizeof(ucnt))
260 return -EINVAL;
261 if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
262 return -EFAULT;
263 if (ucnt == ULLONG_MAX)
264 return -EINVAL;
265 spin_lock_irq(&ctx->wqh.lock);
266 res = -EAGAIN;
267 if (ULLONG_MAX - ctx->count > ucnt)
268 res = sizeof(ucnt);
269 else if (!(file->f_flags & O_NONBLOCK)) {
270 __add_wait_queue(&ctx->wqh, &wait);
271 for (res = 0;;) {
272 set_current_state(TASK_INTERRUPTIBLE);
273 if (ULLONG_MAX - ctx->count > ucnt) {
274 res = sizeof(ucnt);
275 break;
276 }
277 if (signal_pending(current)) {
278 res = -ERESTARTSYS;
279 break;
280 }
281 spin_unlock_irq(&ctx->wqh.lock);
282 schedule();
283 spin_lock_irq(&ctx->wqh.lock);
284 }
285 __remove_wait_queue(&ctx->wqh, &wait);
286 __set_current_state(TASK_RUNNING);
287 }
288 if (likely(res > 0)) {
289 ctx->count += ucnt;
290 if (waitqueue_active(&ctx->wqh))
291 wake_up_locked_poll(&ctx->wqh, EPOLLIN);
292 }
293 spin_unlock_irq(&ctx->wqh.lock);
294
295 return res;
296}
297
298#ifdef CONFIG_PROC_FS
299static void eventfd_show_fdinfo(struct seq_file *m, struct file *f)
300{
301 struct eventfd_ctx *ctx = f->private_data;
302
303 spin_lock_irq(&ctx->wqh.lock);
304 seq_printf(m, "eventfd-count: %16llx\n",
305 (unsigned long long)ctx->count);
306 spin_unlock_irq(&ctx->wqh.lock);
307 seq_printf(m, "eventfd-id: %d\n", ctx->id);
308}
309#endif
310
311static const struct file_operations eventfd_fops = {
312#ifdef CONFIG_PROC_FS
313 .show_fdinfo = eventfd_show_fdinfo,
314#endif
315 .release = eventfd_release,
316 .poll = eventfd_poll,
317 .read = eventfd_read,
318 .write = eventfd_write,
319 .llseek = noop_llseek,
320};
321
322/**
323 * eventfd_fget - Acquire a reference of an eventfd file descriptor.
324 * @fd: [in] Eventfd file descriptor.
325 *
326 * Returns a pointer to the eventfd file structure in case of success, or the
327 * following error pointer:
328 *
329 * -EBADF : Invalid @fd file descriptor.
330 * -EINVAL : The @fd file descriptor is not an eventfd file.
331 */
332struct file *eventfd_fget(int fd)
333{
334 struct file *file;
335
336 file = fget(fd);
337 if (!file)
338 return ERR_PTR(-EBADF);
339 if (file->f_op != &eventfd_fops) {
340 fput(file);
341 return ERR_PTR(-EINVAL);
342 }
343
344 return file;
345}
346EXPORT_SYMBOL_GPL(eventfd_fget);
347
348/**
349 * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
350 * @fd: [in] Eventfd file descriptor.
351 *
352 * Returns a pointer to the internal eventfd context, otherwise the error
353 * pointers returned by the following functions:
354 *
355 * eventfd_fget
356 */
357struct eventfd_ctx *eventfd_ctx_fdget(int fd)
358{
359 struct eventfd_ctx *ctx;
360 struct fd f = fdget(fd);
361 if (!f.file)
362 return ERR_PTR(-EBADF);
363 ctx = eventfd_ctx_fileget(f.file);
364 fdput(f);
365 return ctx;
366}
367EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
368
369/**
370 * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
371 * @file: [in] Eventfd file pointer.
372 *
373 * Returns a pointer to the internal eventfd context, otherwise the error
374 * pointer:
375 *
376 * -EINVAL : The @fd file descriptor is not an eventfd file.
377 */
378struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
379{
380 struct eventfd_ctx *ctx;
381
382 if (file->f_op != &eventfd_fops)
383 return ERR_PTR(-EINVAL);
384
385 ctx = file->private_data;
386 kref_get(&ctx->kref);
387 return ctx;
388}
389EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
390
391static int do_eventfd(unsigned int count, int flags)
392{
393 struct eventfd_ctx *ctx;
394 int fd;
395
396 /* Check the EFD_* constants for consistency. */
397 BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
398 BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
399
400 if (flags & ~EFD_FLAGS_SET)
401 return -EINVAL;
402
403 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
404 if (!ctx)
405 return -ENOMEM;
406
407 kref_init(&ctx->kref);
408 init_waitqueue_head(&ctx->wqh);
409 ctx->count = count;
410 ctx->flags = flags;
411 ctx->id = ida_simple_get(&eventfd_ida, 0, 0, GFP_KERNEL);
412
413 fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx,
414 O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
415 if (fd < 0)
416 eventfd_free_ctx(ctx);
417
418 return fd;
419}
420
421SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
422{
423 return do_eventfd(count, flags);
424}
425
426SYSCALL_DEFINE1(eventfd, unsigned int, count)
427{
428 return do_eventfd(count, 0);
429}
430