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