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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 returining a POLLERR
49 * to poll(2).
50 *
51 * Returns the amount by which the counter was incrememnted. 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 unsigned long flags;
122
123 poll_wait(file, &ctx->wqh, wait);
124
125 spin_lock_irqsave(&ctx->wqh.lock, flags);
126 if (ctx->count > 0)
127 events |= POLLIN;
128 if (ctx->count == ULLONG_MAX)
129 events |= POLLERR;
130 if (ULLONG_MAX - 1 > ctx->count)
131 events |= POLLOUT;
132 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
133
134 return events;
135}
136
137static void eventfd_ctx_do_read(struct eventfd_ctx *ctx, __u64 *cnt)
138{
139 *cnt = (ctx->flags & EFD_SEMAPHORE) ? 1 : ctx->count;
140 ctx->count -= *cnt;
141}
142
143/**
144 * eventfd_ctx_remove_wait_queue - Read the current counter and removes wait queue.
145 * @ctx: [in] Pointer to eventfd context.
146 * @wait: [in] Wait queue to be removed.
147 * @cnt: [out] Pointer to the 64-bit counter value.
148 *
149 * Returns %0 if successful, or the following error codes:
150 *
151 * -EAGAIN : The operation would have blocked.
152 *
153 * This is used to atomically remove a wait queue entry from the eventfd wait
154 * queue head, and read/reset the counter value.
155 */
156int eventfd_ctx_remove_wait_queue(struct eventfd_ctx *ctx, wait_queue_t *wait,
157 __u64 *cnt)
158{
159 unsigned long flags;
160
161 spin_lock_irqsave(&ctx->wqh.lock, flags);
162 eventfd_ctx_do_read(ctx, cnt);
163 __remove_wait_queue(&ctx->wqh, wait);
164 if (*cnt != 0 && waitqueue_active(&ctx->wqh))
165 wake_up_locked_poll(&ctx->wqh, POLLOUT);
166 spin_unlock_irqrestore(&ctx->wqh.lock, flags);
167
168 return *cnt != 0 ? 0 : -EAGAIN;
169}
170EXPORT_SYMBOL_GPL(eventfd_ctx_remove_wait_queue);
171
172/**
173 * eventfd_ctx_read - Reads the eventfd counter or wait if it is zero.
174 * @ctx: [in] Pointer to eventfd context.
175 * @no_wait: [in] Different from zero if the operation should not block.
176 * @cnt: [out] Pointer to the 64-bit counter value.
177 *
178 * Returns %0 if successful, or the following error codes:
179 *
180 * -EAGAIN : The operation would have blocked but @no_wait was non-zero.
181 * -ERESTARTSYS : A signal interrupted the wait operation.
182 *
183 * If @no_wait is zero, the function might sleep until the eventfd internal
184 * counter becomes greater than zero.
185 */
186ssize_t eventfd_ctx_read(struct eventfd_ctx *ctx, int no_wait, __u64 *cnt)
187{
188 ssize_t res;
189 DECLARE_WAITQUEUE(wait, current);
190
191 spin_lock_irq(&ctx->wqh.lock);
192 *cnt = 0;
193 res = -EAGAIN;
194 if (ctx->count > 0)
195 res = 0;
196 else if (!no_wait) {
197 __add_wait_queue(&ctx->wqh, &wait);
198 for (;;) {
199 set_current_state(TASK_INTERRUPTIBLE);
200 if (ctx->count > 0) {
201 res = 0;
202 break;
203 }
204 if (signal_pending(current)) {
205 res = -ERESTARTSYS;
206 break;
207 }
208 spin_unlock_irq(&ctx->wqh.lock);
209 schedule();
210 spin_lock_irq(&ctx->wqh.lock);
211 }
212 __remove_wait_queue(&ctx->wqh, &wait);
213 __set_current_state(TASK_RUNNING);
214 }
215 if (likely(res == 0)) {
216 eventfd_ctx_do_read(ctx, cnt);
217 if (waitqueue_active(&ctx->wqh))
218 wake_up_locked_poll(&ctx->wqh, POLLOUT);
219 }
220 spin_unlock_irq(&ctx->wqh.lock);
221
222 return res;
223}
224EXPORT_SYMBOL_GPL(eventfd_ctx_read);
225
226static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
227 loff_t *ppos)
228{
229 struct eventfd_ctx *ctx = file->private_data;
230 ssize_t res;
231 __u64 cnt;
232
233 if (count < sizeof(cnt))
234 return -EINVAL;
235 res = eventfd_ctx_read(ctx, file->f_flags & O_NONBLOCK, &cnt);
236 if (res < 0)
237 return res;
238
239 return put_user(cnt, (__u64 __user *) buf) ? -EFAULT : sizeof(cnt);
240}
241
242static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
243 loff_t *ppos)
244{
245 struct eventfd_ctx *ctx = file->private_data;
246 ssize_t res;
247 __u64 ucnt;
248 DECLARE_WAITQUEUE(wait, current);
249
250 if (count < sizeof(ucnt))
251 return -EINVAL;
252 if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
253 return -EFAULT;
254 if (ucnt == ULLONG_MAX)
255 return -EINVAL;
256 spin_lock_irq(&ctx->wqh.lock);
257 res = -EAGAIN;
258 if (ULLONG_MAX - ctx->count > ucnt)
259 res = sizeof(ucnt);
260 else if (!(file->f_flags & O_NONBLOCK)) {
261 __add_wait_queue(&ctx->wqh, &wait);
262 for (res = 0;;) {
263 set_current_state(TASK_INTERRUPTIBLE);
264 if (ULLONG_MAX - ctx->count > ucnt) {
265 res = sizeof(ucnt);
266 break;
267 }
268 if (signal_pending(current)) {
269 res = -ERESTARTSYS;
270 break;
271 }
272 spin_unlock_irq(&ctx->wqh.lock);
273 schedule();
274 spin_lock_irq(&ctx->wqh.lock);
275 }
276 __remove_wait_queue(&ctx->wqh, &wait);
277 __set_current_state(TASK_RUNNING);
278 }
279 if (likely(res > 0)) {
280 ctx->count += ucnt;
281 if (waitqueue_active(&ctx->wqh))
282 wake_up_locked_poll(&ctx->wqh, POLLIN);
283 }
284 spin_unlock_irq(&ctx->wqh.lock);
285
286 return res;
287}
288
289#ifdef CONFIG_PROC_FS
290static int eventfd_show_fdinfo(struct seq_file *m, struct file *f)
291{
292 struct eventfd_ctx *ctx = f->private_data;
293 int ret;
294
295 spin_lock_irq(&ctx->wqh.lock);
296 ret = seq_printf(m, "eventfd-count: %16llx\n",
297 (unsigned long long)ctx->count);
298 spin_unlock_irq(&ctx->wqh.lock);
299
300 return ret;
301}
302#endif
303
304static const struct file_operations eventfd_fops = {
305#ifdef CONFIG_PROC_FS
306 .show_fdinfo = eventfd_show_fdinfo,
307#endif
308 .release = eventfd_release,
309 .poll = eventfd_poll,
310 .read = eventfd_read,
311 .write = eventfd_write,
312 .llseek = noop_llseek,
313};
314
315/**
316 * eventfd_fget - Acquire a reference of an eventfd file descriptor.
317 * @fd: [in] Eventfd file descriptor.
318 *
319 * Returns a pointer to the eventfd file structure in case of success, or the
320 * following error pointer:
321 *
322 * -EBADF : Invalid @fd file descriptor.
323 * -EINVAL : The @fd file descriptor is not an eventfd file.
324 */
325struct file *eventfd_fget(int fd)
326{
327 struct file *file;
328
329 file = fget(fd);
330 if (!file)
331 return ERR_PTR(-EBADF);
332 if (file->f_op != &eventfd_fops) {
333 fput(file);
334 return ERR_PTR(-EINVAL);
335 }
336
337 return file;
338}
339EXPORT_SYMBOL_GPL(eventfd_fget);
340
341/**
342 * eventfd_ctx_fdget - Acquires a reference to the internal eventfd context.
343 * @fd: [in] Eventfd file descriptor.
344 *
345 * Returns a pointer to the internal eventfd context, otherwise the error
346 * pointers returned by the following functions:
347 *
348 * eventfd_fget
349 */
350struct eventfd_ctx *eventfd_ctx_fdget(int fd)
351{
352 struct eventfd_ctx *ctx;
353 struct fd f = fdget(fd);
354 if (!f.file)
355 return ERR_PTR(-EBADF);
356 ctx = eventfd_ctx_fileget(f.file);
357 fdput(f);
358 return ctx;
359}
360EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);
361
362/**
363 * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.
364 * @file: [in] Eventfd file pointer.
365 *
366 * Returns a pointer to the internal eventfd context, otherwise the error
367 * pointer:
368 *
369 * -EINVAL : The @fd file descriptor is not an eventfd file.
370 */
371struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)
372{
373 if (file->f_op != &eventfd_fops)
374 return ERR_PTR(-EINVAL);
375
376 return eventfd_ctx_get(file->private_data);
377}
378EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);
379
380/**
381 * eventfd_file_create - Creates an eventfd file pointer.
382 * @count: Initial eventfd counter value.
383 * @flags: Flags for the eventfd file.
384 *
385 * This function creates an eventfd file pointer, w/out installing it into
386 * the fd table. This is useful when the eventfd file is used during the
387 * initialization of data structures that require extra setup after the eventfd
388 * creation. So the eventfd creation is split into the file pointer creation
389 * phase, and the file descriptor installation phase.
390 * In this way races with userspace closing the newly installed file descriptor
391 * can be avoided.
392 * Returns an eventfd file pointer, or a proper error pointer.
393 */
394struct file *eventfd_file_create(unsigned int count, int flags)
395{
396 struct file *file;
397 struct eventfd_ctx *ctx;
398
399 /* Check the EFD_* constants for consistency. */
400 BUILD_BUG_ON(EFD_CLOEXEC != O_CLOEXEC);
401 BUILD_BUG_ON(EFD_NONBLOCK != O_NONBLOCK);
402
403 if (flags & ~EFD_FLAGS_SET)
404 return ERR_PTR(-EINVAL);
405
406 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
407 if (!ctx)
408 return ERR_PTR(-ENOMEM);
409
410 kref_init(&ctx->kref);
411 init_waitqueue_head(&ctx->wqh);
412 ctx->count = count;
413 ctx->flags = flags;
414
415 file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx,
416 O_RDWR | (flags & EFD_SHARED_FCNTL_FLAGS));
417 if (IS_ERR(file))
418 eventfd_free_ctx(ctx);
419
420 return file;
421}
422
423SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)
424{
425 int fd, error;
426 struct file *file;
427
428 error = get_unused_fd_flags(flags & EFD_SHARED_FCNTL_FLAGS);
429 if (error < 0)
430 return error;
431 fd = error;
432
433 file = eventfd_file_create(count, flags);
434 if (IS_ERR(file)) {
435 error = PTR_ERR(file);
436 goto err_put_unused_fd;
437 }
438 fd_install(fd, file);
439
440 return fd;
441
442err_put_unused_fd:
443 put_unused_fd(fd);
444
445 return error;
446}
447
448SYSCALL_DEFINE1(eventfd, unsigned int, count)
449{
450 return sys_eventfd2(count, 0);
451}
452