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1// SPDX-License-Identifier: GPL-2.0-only2/*3 * fs/eventfd.c4 *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, the35 * value of the __u64 being written is added to "count" and a36 * wakeup is performed on "wqh". If EFD_SEMAPHORE flag was not37 * 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 counter48 * @ctx: [in] Pointer to the eventfd context.49 * @mask: [in] poll mask50 *51 * This function is supposed to be called by the kernel in paths that do not52 * allow sleeping. In this function we allow the counter to reach the ULLONG_MAX53 * value, and we signal this as overflow condition by returning a EPOLLERR54 * 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 here62 * through waitqueue wakeup handlers. If the caller users potentially63 * nested waitqueues with custom wakeup handlers, then it should64 * check eventfd_signal_allowed() before calling this function. If65 * it returns false, the eventfd_signal() call should be deferred to a66 * 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 either101 * 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 HWJS_SUSPENDS 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 read128 * can be done outside ctx->wqh.lock because we know that poll_wait129 * takes that lock (through add_wait_queue) if our caller will sleep.130 *131 * The read _can_ therefore seep into add_wait_queue's critical132 * section, but cannot move above it! add_wait_queue's spin_lock acts133 * as an acquire barrier and ensures that the read be ordered properly134 * against the writes. The following CAN happen and is safe:135 *136 * poll write137 * ----------------- ------------138 * lock ctx->wqh.lock (in poll_wait)139 * count = ctx->count140 * __add_wait_queue141 * unlock ctx->wqh.lock142 * lock ctx->qwh.lock143 * ctx->count += n144 * if (waitqueue_active)145 * wake_up_locked_poll146 * unlock ctx->qwh.lock147 * eventfd_poll returns 0148 *149 * but the following, which would miss a wakeup, cannot happen:150 *151 * poll write152 * ----------------- ------------153 * count = ctx->count (INVALID!)154 * lock ctx->qwh.lock155 * ctx->count += n156 * **waitqueue_active is false**157 * **no wake_up_locked_poll!**158 * unlock ctx->qwh.lock159 * lock ctx->wqh.lock (in poll_wait)160 * __add_wait_queue161 * unlock ctx->wqh.lock162 * eventfd_poll returns 0163 */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 wait196 * 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 HWJS_SUSPENDS 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 HWJS_SUSPENDS 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_FS283static 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#endif301 302static const struct file_operations eventfd_fops = {303#ifdef CONFIG_PROC_FS304 .show_fdinfo = eventfd_show_fdinfo,305#endif306 .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 the318 * 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 error344 * pointers returned by the following functions:345 *346 * eventfd_fget347 */348struct eventfd_ctx *eventfd_ctx_fdget(int fd)349{350 struct eventfd_ctx *ctx;351 struct fd f = fdget(fd);352 if (!fd_file(f))353 return ERR_PTR(-EBADF);354 ctx = eventfd_ctx_fileget(fd_file(f));355 fdput(f);356 return ctx;357}358EXPORT_SYMBOL_GPL(eventfd_ctx_fdget);359 360/**361 * eventfd_ctx_fileget - Acquires a reference to the internal eventfd context.362 * @file: [in] Eventfd file pointer.363 *364 * Returns a pointer to the internal eventfd context, otherwise the error365 * pointer:366 *367 * -EINVAL : The @fd file descriptor is not an eventfd file.368 */369struct eventfd_ctx *eventfd_ctx_fileget(struct file *file)370{371 struct eventfd_ctx *ctx;372 373 if (file->f_op != &eventfd_fops)374 return ERR_PTR(-EINVAL);375 376 ctx = file->private_data;377 kref_get(&ctx->kref);378 return ctx;379}380EXPORT_SYMBOL_GPL(eventfd_ctx_fileget);381 382static HWJS_SUSPENDS int do_eventfd(unsigned int count, int flags)383{384 struct eventfd_ctx *ctx;385 struct file *file;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 BUILD_BUG_ON(EFD_SEMAPHORE != (1 << 0));392 393 if (flags & ~EFD_FLAGS_SET)394 return -EINVAL;395 396 ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);397 if (!ctx)398 return -ENOMEM;399 400 kref_init(&ctx->kref);401 init_waitqueue_head(&ctx->wqh);402 ctx->count = count;403 ctx->flags = flags;404 ctx->id = ida_alloc(&eventfd_ida, GFP_KERNEL);405 406 flags &= EFD_SHARED_FCNTL_FLAGS;407 flags |= O_RDWR;408 fd = get_unused_fd_flags(flags);409 if (fd < 0)410 goto err;411 412 file = anon_inode_getfile("[eventfd]", &eventfd_fops, ctx, flags);413 if (IS_ERR(file)) {414 put_unused_fd(fd);415 fd = PTR_ERR(file);416 goto err;417 }418 419 file->f_mode |= FMODE_NOWAIT;420 fd_install(fd, file);421 return fd;422err:423 eventfd_free_ctx(ctx);424 return fd;425}426 427SYSCALL_DEFINE2(eventfd2, unsigned int, count, int, flags)428{429 return do_eventfd(count, flags);430}431 432SYSCALL_DEFINE1(eventfd, unsigned int, count)433{434 return do_eventfd(count, 0);435}436 437