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18963c01b8
The timerfd was using the unlocked waitqueue operations, but it was using a different lock, so poll_wait() would race with it. This makes timerfd directly use the waitqueue lock. Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
226 lines
5.0 KiB
C
226 lines
5.0 KiB
C
/*
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* fs/timerfd.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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* Thanks to Thomas Gleixner for code reviews and useful comments.
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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/time.h>
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#include <linux/hrtimer.h>
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#include <linux/anon_inodes.h>
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#include <linux/timerfd.h>
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struct timerfd_ctx {
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struct hrtimer tmr;
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ktime_t tintv;
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wait_queue_head_t wqh;
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int expired;
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};
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/*
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* This gets called when the timer event triggers. We set the "expired"
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* flag, but we do not re-arm the timer (in case it's necessary,
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* tintv.tv64 != 0) until the timer is read.
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*/
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static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
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{
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struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
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unsigned long flags;
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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ctx->expired = 1;
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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 HRTIMER_NORESTART;
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}
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static void timerfd_setup(struct timerfd_ctx *ctx, int clockid, int flags,
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const struct itimerspec *ktmr)
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{
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enum hrtimer_mode htmode;
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ktime_t texp;
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htmode = (flags & TFD_TIMER_ABSTIME) ?
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HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
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texp = timespec_to_ktime(ktmr->it_value);
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ctx->expired = 0;
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ctx->tintv = timespec_to_ktime(ktmr->it_interval);
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hrtimer_init(&ctx->tmr, clockid, htmode);
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ctx->tmr.expires = texp;
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ctx->tmr.function = timerfd_tmrproc;
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if (texp.tv64 != 0)
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hrtimer_start(&ctx->tmr, texp, htmode);
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}
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static int timerfd_release(struct inode *inode, struct file *file)
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{
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struct timerfd_ctx *ctx = file->private_data;
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hrtimer_cancel(&ctx->tmr);
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kfree(ctx);
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return 0;
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}
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static unsigned int timerfd_poll(struct file *file, poll_table *wait)
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{
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struct timerfd_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->expired)
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events |= POLLIN;
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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 timerfd_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 timerfd_ctx *ctx = file->private_data;
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ssize_t res;
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u32 ticks = 0;
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DECLARE_WAITQUEUE(wait, current);
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if (count < sizeof(ticks))
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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 (!ctx->expired && !(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->expired) {
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res = 0;
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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 (ctx->expired) {
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ctx->expired = 0;
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if (ctx->tintv.tv64 != 0) {
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/*
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* If tintv.tv64 != 0, this is a periodic timer that
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* needs to be re-armed. We avoid doing it in the timer
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* callback to avoid DoS attacks specifying a very
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* short timer period.
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*/
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ticks = (u32)
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hrtimer_forward(&ctx->tmr,
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hrtimer_cb_get_time(&ctx->tmr),
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ctx->tintv);
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hrtimer_restart(&ctx->tmr);
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} else
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ticks = 1;
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}
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spin_unlock_irq(&ctx->wqh.lock);
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if (ticks)
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res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks);
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return res;
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}
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static const struct file_operations timerfd_fops = {
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.release = timerfd_release,
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.poll = timerfd_poll,
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.read = timerfd_read,
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};
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asmlinkage long sys_timerfd(int ufd, int clockid, int flags,
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const struct itimerspec __user *utmr)
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{
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int error;
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struct timerfd_ctx *ctx;
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struct file *file;
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struct inode *inode;
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struct itimerspec ktmr;
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if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
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return -EFAULT;
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if (clockid != CLOCK_MONOTONIC &&
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clockid != CLOCK_REALTIME)
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return -EINVAL;
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if (!timespec_valid(&ktmr.it_value) ||
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!timespec_valid(&ktmr.it_interval))
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return -EINVAL;
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if (ufd == -1) {
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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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timerfd_setup(ctx, clockid, flags, &ktmr);
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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(&ufd, &inode, &file, "[timerfd]",
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&timerfd_fops, ctx);
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if (error)
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goto err_tmrcancel;
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} else {
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file = fget(ufd);
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if (!file)
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return -EBADF;
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ctx = file->private_data;
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if (file->f_op != &timerfd_fops) {
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fput(file);
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return -EINVAL;
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}
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/*
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* We need to stop the existing timer before reprogramming
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* it to the new values.
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*/
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for (;;) {
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spin_lock_irq(&ctx->wqh.lock);
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if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
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break;
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spin_unlock_irq(&ctx->wqh.lock);
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cpu_relax();
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}
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/*
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* Re-program the timer to the new value ...
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*/
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timerfd_setup(ctx, clockid, flags, &ktmr);
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spin_unlock_irq(&ctx->wqh.lock);
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fput(file);
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}
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return ufd;
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err_tmrcancel:
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hrtimer_cancel(&ctx->tmr);
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kfree(ctx);
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return error;
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}
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