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![Max Asbock](/assets/img/avatar_default.png)
Currently processes waiting with poll on cancelable timerfd timers are not woken up when the timers are canceled. When the system time is set the clock_was_set() function calls timerfd_clock_was_set() to cancel and wake up processes waiting on potential cancelable timerfd timers. However the wake up currently has no effect because in the case of timerfd_read it is dependent on ctx->ticks not being 0. timerfd_poll also requires ctx->ticks being non zero. As a consequence processes waiting on cancelable timers only get woken up when the timers expire. This patch fixes this by incrementing ctx->ticks before calling wake_up. Signed-off-by: Max Asbock <masbock@linux.vnet.ibm.com> Cc: kay.sievers@vrfy.org Cc: virtuoso@slind.org Cc: johnstul <johnstul@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1307985512.4710.41.camel@w-amax.beaverton.ibm.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
369 lines
8.6 KiB
C
369 lines
8.6 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/slab.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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#include <linux/syscalls.h>
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#include <linux/rcupdate.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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ktime_t moffs;
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wait_queue_head_t wqh;
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u64 ticks;
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int expired;
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int clockid;
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struct rcu_head rcu;
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struct list_head clist;
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bool might_cancel;
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};
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static LIST_HEAD(cancel_list);
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static DEFINE_SPINLOCK(cancel_lock);
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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 accessed.
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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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ctx->ticks++;
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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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/*
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* Called when the clock was set to cancel the timers in the cancel
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* list. This will wake up processes waiting on these timers. The
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* wake-up requires ctx->ticks to be non zero, therefore we increment
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* it before calling wake_up_locked().
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*/
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void timerfd_clock_was_set(void)
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{
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ktime_t moffs = ktime_get_monotonic_offset();
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struct timerfd_ctx *ctx;
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unsigned long flags;
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rcu_read_lock();
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list_for_each_entry_rcu(ctx, &cancel_list, clist) {
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if (!ctx->might_cancel)
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continue;
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spin_lock_irqsave(&ctx->wqh.lock, flags);
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if (ctx->moffs.tv64 != moffs.tv64) {
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ctx->moffs.tv64 = KTIME_MAX;
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ctx->ticks++;
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wake_up_locked(&ctx->wqh);
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}
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spin_unlock_irqrestore(&ctx->wqh.lock, flags);
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}
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rcu_read_unlock();
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}
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static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
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{
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if (ctx->might_cancel) {
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ctx->might_cancel = false;
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spin_lock(&cancel_lock);
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list_del_rcu(&ctx->clist);
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spin_unlock(&cancel_lock);
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}
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}
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static bool timerfd_canceled(struct timerfd_ctx *ctx)
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{
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if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
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return false;
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ctx->moffs = ktime_get_monotonic_offset();
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return true;
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}
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static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
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{
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if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
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(flags & TFD_TIMER_CANCEL_ON_SET)) {
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if (!ctx->might_cancel) {
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ctx->might_cancel = true;
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spin_lock(&cancel_lock);
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list_add_rcu(&ctx->clist, &cancel_list);
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spin_unlock(&cancel_lock);
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}
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} else if (ctx->might_cancel) {
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timerfd_remove_cancel(ctx);
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}
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}
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static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
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{
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ktime_t remaining;
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remaining = hrtimer_expires_remaining(&ctx->tmr);
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return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
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}
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static int timerfd_setup(struct timerfd_ctx *ctx, 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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int clockid = ctx->clockid;
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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->ticks = 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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hrtimer_set_expires(&ctx->tmr, 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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if (timerfd_canceled(ctx))
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return -ECANCELED;
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}
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return 0;
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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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timerfd_remove_cancel(ctx);
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hrtimer_cancel(&ctx->tmr);
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kfree_rcu(ctx, rcu);
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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->ticks)
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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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u64 ticks = 0;
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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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if (file->f_flags & O_NONBLOCK)
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res = -EAGAIN;
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else
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res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
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/*
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* If clock has changed, we do not care about the
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* ticks and we do not rearm the timer. Userspace must
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* reevaluate anyway.
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*/
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if (timerfd_canceled(ctx)) {
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ctx->ticks = 0;
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ctx->expired = 0;
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res = -ECANCELED;
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}
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if (ctx->ticks) {
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ticks = ctx->ticks;
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if (ctx->expired && ctx->tintv.tv64) {
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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 += hrtimer_forward_now(&ctx->tmr,
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ctx->tintv) - 1;
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hrtimer_restart(&ctx->tmr);
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}
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ctx->expired = 0;
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ctx->ticks = 0;
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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, (u64 __user *) 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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.llseek = noop_llseek,
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};
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static struct file *timerfd_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 != &timerfd_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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SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
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{
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int ufd;
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struct timerfd_ctx *ctx;
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/* Check the TFD_* constants for consistency. */
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BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
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BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
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if ((flags & ~TFD_CREATE_FLAGS) ||
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(clockid != CLOCK_MONOTONIC &&
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clockid != CLOCK_REALTIME))
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return -EINVAL;
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ctx = kzalloc(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->clockid = clockid;
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hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
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ctx->moffs = ktime_get_monotonic_offset();
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ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
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O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
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if (ufd < 0)
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kfree(ctx);
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return ufd;
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}
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SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
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const struct itimerspec __user *, utmr,
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struct itimerspec __user *, otmr)
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{
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struct file *file;
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struct timerfd_ctx *ctx;
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struct itimerspec ktmr, kotmr;
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int ret;
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if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
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return -EFAULT;
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if ((flags & ~TFD_SETTIME_FLAGS) ||
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!timespec_valid(&ktmr.it_value) ||
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!timespec_valid(&ktmr.it_interval))
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return -EINVAL;
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file = timerfd_fget(ufd);
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if (IS_ERR(file))
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return PTR_ERR(file);
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ctx = file->private_data;
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timerfd_setup_cancel(ctx, flags);
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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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* If the timer is expired and it's periodic, we need to advance it
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* because the caller may want to know the previous expiration time.
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* We do not update "ticks" and "expired" since the timer will be
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* re-programmed again in the following timerfd_setup() call.
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*/
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if (ctx->expired && ctx->tintv.tv64)
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hrtimer_forward_now(&ctx->tmr, ctx->tintv);
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kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
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kotmr.it_interval = ktime_to_timespec(ctx->tintv);
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/*
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* Re-program the timer to the new value ...
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*/
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ret = timerfd_setup(ctx, flags, &ktmr);
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spin_unlock_irq(&ctx->wqh.lock);
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fput(file);
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if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
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return -EFAULT;
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return ret;
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}
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SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
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{
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struct file *file;
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struct timerfd_ctx *ctx;
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struct itimerspec kotmr;
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file = timerfd_fget(ufd);
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if (IS_ERR(file))
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return PTR_ERR(file);
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ctx = file->private_data;
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spin_lock_irq(&ctx->wqh.lock);
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if (ctx->expired && ctx->tintv.tv64) {
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ctx->expired = 0;
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ctx->ticks +=
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hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
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hrtimer_restart(&ctx->tmr);
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}
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kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
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kotmr.it_interval = ktime_to_timespec(ctx->tintv);
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spin_unlock_irq(&ctx->wqh.lock);
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fput(file);
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return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
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}
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