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![Al Viro](/assets/img/avatar_default.png)
a) none of the callers even looks at inode or file returned by anon_inode_getfd() b) any caller that would try to look at those would be racy, since by the time it returns we might have raced with close() from another thread and that file would be pining for fjords. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
222 lines
5 KiB
C
222 lines
5 KiB
C
/*
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* fs/eventfd.c
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*
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* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
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*
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*/
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#include <linux/file.h>
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#include <linux/poll.h>
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/kernel.h>
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#include <linux/list.h>
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#include <linux/spinlock.h>
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#include <linux/anon_inodes.h>
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#include <linux/eventfd.h>
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#include <linux/syscalls.h>
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struct eventfd_ctx {
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wait_queue_head_t wqh;
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/*
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* Every time that a write(2) is performed on an eventfd, the
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* value of the __u64 being written is added to "count" and a
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* wakeup is performed on "wqh". A read(2) will return the "count"
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* value to userspace, and will reset "count" to zero. The kernel
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* size eventfd_signal() also, adds to the "count" counter and
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* issue a wakeup.
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*/
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__u64 count;
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};
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/*
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* Adds "n" to the eventfd counter "count". Returns "n" in case of
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* success, or a value lower then "n" in case of coutner overflow.
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* This function is supposed to be called by the kernel in paths
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* that do not allow sleeping. In this function we allow the counter
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* to reach the ULLONG_MAX value, and we signal this as overflow
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* condition by returining a POLLERR to poll(2).
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*/
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int eventfd_signal(struct file *file, int n)
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{
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struct eventfd_ctx *ctx = file->private_data;
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unsigned long flags;
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if (n < 0)
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return -EINVAL;
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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if (ULLONG_MAX - ctx->count < n)
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n = (int) (ULLONG_MAX - ctx->count);
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ctx->count += n;
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked(&ctx->wqh);
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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return n;
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}
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static int eventfd_release(struct inode *inode, struct file *file)
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{
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kfree(file->private_data);
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return 0;
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}
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static unsigned int eventfd_poll(struct file *file, poll_table *wait)
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{
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struct eventfd_ctx *ctx = file->private_data;
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unsigned int events = 0;
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unsigned long flags;
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poll_wait(file, &ctx->wqh, wait);
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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if (ctx->count > 0)
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events |= POLLIN;
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if (ctx->count == ULLONG_MAX)
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events |= POLLERR;
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if (ULLONG_MAX - 1 > ctx->count)
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events |= POLLOUT;
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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return events;
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}
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static ssize_t eventfd_read(struct file *file, char __user *buf, size_t count,
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loff_t *ppos)
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{
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struct eventfd_ctx *ctx = file->private_data;
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ssize_t res;
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__u64 ucnt;
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DECLARE_WAITQUEUE(wait, current);
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if (count < sizeof(ucnt))
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return -EINVAL;
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spin_lock_irq(&ctx->wqh.lock);
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res = -EAGAIN;
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ucnt = ctx->count;
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if (ucnt > 0)
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res = sizeof(ucnt);
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else if (!(file->f_flags & O_NONBLOCK)) {
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__add_wait_queue(&ctx->wqh, &wait);
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for (res = 0;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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if (ctx->count > 0) {
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ucnt = ctx->count;
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res = sizeof(ucnt);
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break;
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}
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if (signal_pending(current)) {
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res = -ERESTARTSYS;
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break;
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}
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spin_unlock_irq(&ctx->wqh.lock);
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schedule();
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spin_lock_irq(&ctx->wqh.lock);
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}
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__remove_wait_queue(&ctx->wqh, &wait);
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__set_current_state(TASK_RUNNING);
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}
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if (res > 0) {
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ctx->count = 0;
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked(&ctx->wqh);
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}
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spin_unlock_irq(&ctx->wqh.lock);
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if (res > 0 && put_user(ucnt, (__u64 __user *) buf))
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return -EFAULT;
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return res;
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}
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static ssize_t eventfd_write(struct file *file, const char __user *buf, size_t count,
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loff_t *ppos)
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{
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struct eventfd_ctx *ctx = file->private_data;
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ssize_t res;
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__u64 ucnt;
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DECLARE_WAITQUEUE(wait, current);
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if (count < sizeof(ucnt))
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return -EINVAL;
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if (copy_from_user(&ucnt, buf, sizeof(ucnt)))
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return -EFAULT;
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if (ucnt == ULLONG_MAX)
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return -EINVAL;
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spin_lock_irq(&ctx->wqh.lock);
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res = -EAGAIN;
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if (ULLONG_MAX - ctx->count > ucnt)
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res = sizeof(ucnt);
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else if (!(file->f_flags & O_NONBLOCK)) {
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__add_wait_queue(&ctx->wqh, &wait);
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for (res = 0;;) {
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set_current_state(TASK_INTERRUPTIBLE);
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if (ULLONG_MAX - ctx->count > ucnt) {
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res = sizeof(ucnt);
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break;
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}
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if (signal_pending(current)) {
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res = -ERESTARTSYS;
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break;
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}
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spin_unlock_irq(&ctx->wqh.lock);
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schedule();
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spin_lock_irq(&ctx->wqh.lock);
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}
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__remove_wait_queue(&ctx->wqh, &wait);
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__set_current_state(TASK_RUNNING);
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}
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if (res > 0) {
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ctx->count += ucnt;
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if (waitqueue_active(&ctx->wqh))
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wake_up_locked(&ctx->wqh);
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}
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spin_unlock_irq(&ctx->wqh.lock);
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return res;
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}
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static const struct file_operations eventfd_fops = {
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.release = eventfd_release,
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.poll = eventfd_poll,
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.read = eventfd_read,
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.write = eventfd_write,
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};
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struct file *eventfd_fget(int fd)
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{
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struct file *file;
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file = fget(fd);
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if (!file)
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return ERR_PTR(-EBADF);
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if (file->f_op != &eventfd_fops) {
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fput(file);
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return ERR_PTR(-EINVAL);
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}
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return file;
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}
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asmlinkage long sys_eventfd(unsigned int count)
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{
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int fd;
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struct eventfd_ctx *ctx;
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ctx = kmalloc(sizeof(*ctx), GFP_KERNEL);
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if (!ctx)
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return -ENOMEM;
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init_waitqueue_head(&ctx->wqh);
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ctx->count = count;
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/*
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* When we call this, the initialization must be complete, since
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* anon_inode_getfd() will install the fd.
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*/
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fd = anon_inode_getfd("[eventfd]", &eventfd_fops, ctx);
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if (fd < 0)
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kfree(ctx);
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return fd;
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}
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