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![Davide Libenzi](/assets/img/avatar_default.png)
The eventfd was using the unlocked waitqueue operations, but it was using a different lock, so poll_wait() would race with it. This makes eventfd directly use the waitqueue lock. Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
226 lines
5.1 KiB
C
226 lines
5.1 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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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 error, fd;
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struct eventfd_ctx *ctx;
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struct file *file;
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struct inode *inode;
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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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error = anon_inode_getfd(&fd, &inode, &file, "[eventfd]",
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&eventfd_fops, ctx);
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if (!error)
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return fd;
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kfree(ctx);
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return error;
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}
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