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/*
* fs/timerfd.c
*
* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
*
*
* Thanks to Thomas Gleixner for code reviews and useful comments.
*
*/
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/time.h>
#include <linux/hrtimer.h>
#include <linux/anon_inodes.h>
#include <linux/timerfd.h>
#include <linux/syscalls.h>
#include <linux/rcupdate.h>
struct timerfd_ctx {
struct hrtimer tmr;
ktime_t tintv;
ktime_t moffs;
wait_queue_head_t wqh;
u64 ticks;
int expired;
int clockid;
struct rcu_head rcu;
struct list_head clist;
bool might_cancel;
};
static LIST_HEAD(cancel_list);
static DEFINE_SPINLOCK(cancel_lock);
/*
* This gets called when the timer event triggers. We set the "expired"
* flag, but we do not re-arm the timer (in case it's necessary,
* tintv.tv64 != 0) until the timer is accessed.
*/
static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
{
struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
unsigned long flags;
spin_lock_irqsave(&ctx->wqh.lock, flags);
ctx->expired = 1;
ctx->ticks++;
wake_up_locked(&ctx->wqh);
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return HRTIMER_NORESTART;
}
/*
* Called when the clock was set to cancel the timers in the cancel
* list. This will wake up processes waiting on these timers. The
* wake-up requires ctx->ticks to be non zero, therefore we increment
* it before calling wake_up_locked().
*/
void timerfd_clock_was_set(void)
{
ktime_t moffs = ktime_get_monotonic_offset();
struct timerfd_ctx *ctx;
unsigned long flags;
rcu_read_lock();
list_for_each_entry_rcu(ctx, &cancel_list, clist) {
if (!ctx->might_cancel)
continue;
spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ctx->moffs.tv64 != moffs.tv64) {
ctx->moffs.tv64 = KTIME_MAX;
ctx->ticks++;
wake_up_locked(&ctx->wqh);
}
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
}
rcu_read_unlock();
}
static void timerfd_remove_cancel(struct timerfd_ctx *ctx)
{
if (ctx->might_cancel) {
ctx->might_cancel = false;
spin_lock(&cancel_lock);
list_del_rcu(&ctx->clist);
spin_unlock(&cancel_lock);
}
}
static bool timerfd_canceled(struct timerfd_ctx *ctx)
{
if (!ctx->might_cancel || ctx->moffs.tv64 != KTIME_MAX)
return false;
ctx->moffs = ktime_get_monotonic_offset();
return true;
}
static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
{
if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
(flags & TFD_TIMER_CANCEL_ON_SET)) {
if (!ctx->might_cancel) {
ctx->might_cancel = true;
spin_lock(&cancel_lock);
list_add_rcu(&ctx->clist, &cancel_list);
spin_unlock(&cancel_lock);
}
} else if (ctx->might_cancel) {
timerfd_remove_cancel(ctx);
}
}
static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
{
ktime_t remaining;
remaining = hrtimer_expires_remaining(&ctx->tmr);
return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
}
static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
const struct itimerspec *ktmr)
{
enum hrtimer_mode htmode;
ktime_t texp;
int clockid = ctx->clockid;
htmode = (flags & TFD_TIMER_ABSTIME) ?
HRTIMER_MODE_ABS: HRTIMER_MODE_REL;
texp = timespec_to_ktime(ktmr->it_value);
ctx->expired = 0;
ctx->ticks = 0;
ctx->tintv = timespec_to_ktime(ktmr->it_interval);
hrtimer_init(&ctx->tmr, clockid, htmode);
hrtimer_set_expires(&ctx->tmr, texp);
ctx->tmr.function = timerfd_tmrproc;
if (texp.tv64 != 0) {
hrtimer_start(&ctx->tmr, texp, htmode);
if (timerfd_canceled(ctx))
return -ECANCELED;
}
return 0;
}
static int timerfd_release(struct inode *inode, struct file *file)
{
struct timerfd_ctx *ctx = file->private_data;
timerfd_remove_cancel(ctx);
hrtimer_cancel(&ctx->tmr);
kfree_rcu(ctx, rcu);
return 0;
}
static unsigned int timerfd_poll(struct file *file, poll_table *wait)
{
struct timerfd_ctx *ctx = file->private_data;
unsigned int events = 0;
unsigned long flags;
poll_wait(file, &ctx->wqh, wait);
spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ctx->ticks)
events |= POLLIN;
spin_unlock_irqrestore(&ctx->wqh.lock, flags);
return events;
}
static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
loff_t *ppos)
{
struct timerfd_ctx *ctx = file->private_data;
ssize_t res;
u64 ticks = 0;
if (count < sizeof(ticks))
return -EINVAL;
spin_lock_irq(&ctx->wqh.lock);
if (file->f_flags & O_NONBLOCK)
res = -EAGAIN;
else
res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);
/*
* If clock has changed, we do not care about the
* ticks and we do not rearm the timer. Userspace must
* reevaluate anyway.
*/
if (timerfd_canceled(ctx)) {
ctx->ticks = 0;
ctx->expired = 0;
res = -ECANCELED;
}
if (ctx->ticks) {
ticks = ctx->ticks;
if (ctx->expired && ctx->tintv.tv64) {
/*
* If tintv.tv64 != 0, this is a periodic timer that
* needs to be re-armed. We avoid doing it in the timer
* callback to avoid DoS attacks specifying a very
* short timer period.
*/
ticks += hrtimer_forward_now(&ctx->tmr,
ctx->tintv) - 1;
hrtimer_restart(&ctx->tmr);
}
ctx->expired = 0;
ctx->ticks = 0;
}
spin_unlock_irq(&ctx->wqh.lock);
if (ticks)
res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks);
return res;
}
static const struct file_operations timerfd_fops = {
.release = timerfd_release,
.poll = timerfd_poll,
.read = timerfd_read,
.llseek = noop_llseek,
};
static struct file *timerfd_fget(int fd)
{
struct file *file;
file = fget(fd);
if (!file)
return ERR_PTR(-EBADF);
if (file->f_op != &timerfd_fops) {
fput(file);
return ERR_PTR(-EINVAL);
}
return file;
}
SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
{
int ufd;
struct timerfd_ctx *ctx;
/* Check the TFD_* constants for consistency. */
BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
if ((flags & ~TFD_CREATE_FLAGS) ||
(clockid != CLOCK_MONOTONIC &&
clockid != CLOCK_REALTIME))
return -EINVAL;
ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
if (!ctx)
return -ENOMEM;
init_waitqueue_head(&ctx->wqh);
ctx->clockid = clockid;
hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
ctx->moffs = ktime_get_monotonic_offset();
ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
O_RDWR | (flags & TFD_SHARED_FCNTL_FLAGS));
if (ufd < 0)
kfree(ctx);
return ufd;
}
SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
const struct itimerspec __user *, utmr,
struct itimerspec __user *, otmr)
{
struct file *file;
struct timerfd_ctx *ctx;
struct itimerspec ktmr, kotmr;
int ret;
if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
return -EFAULT;
if ((flags & ~TFD_SETTIME_FLAGS) ||
!timespec_valid(&ktmr.it_value) ||
!timespec_valid(&ktmr.it_interval))
return -EINVAL;
file = timerfd_fget(ufd);
if (IS_ERR(file))
return PTR_ERR(file);
ctx = file->private_data;
timerfd_setup_cancel(ctx, flags);
/*
* We need to stop the existing timer before reprogramming
* it to the new values.
*/
for (;;) {
spin_lock_irq(&ctx->wqh.lock);
if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
break;
spin_unlock_irq(&ctx->wqh.lock);
cpu_relax();
}
/*
* If the timer is expired and it's periodic, we need to advance it
* because the caller may want to know the previous expiration time.
* We do not update "ticks" and "expired" since the timer will be
* re-programmed again in the following timerfd_setup() call.
*/
if (ctx->expired && ctx->tintv.tv64)
hrtimer_forward_now(&ctx->tmr, ctx->tintv);
kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
kotmr.it_interval = ktime_to_timespec(ctx->tintv);
/*
* Re-program the timer to the new value ...
*/
ret = timerfd_setup(ctx, flags, &ktmr);
spin_unlock_irq(&ctx->wqh.lock);
fput(file);
if (otmr && copy_to_user(otmr, &kotmr, sizeof(kotmr)))
return -EFAULT;
return ret;
}
SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
{
struct file *file;
struct timerfd_ctx *ctx;
struct itimerspec kotmr;
file = timerfd_fget(ufd);
if (IS_ERR(file))
return PTR_ERR(file);
ctx = file->private_data;
spin_lock_irq(&ctx->wqh.lock);
if (ctx->expired && ctx->tintv.tv64) {
ctx->expired = 0;
ctx->ticks +=
hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
hrtimer_restart(&ctx->tmr);
}
kotmr.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
kotmr.it_interval = ktime_to_timespec(ctx->tintv);
spin_unlock_irq(&ctx->wqh.lock);
fput(file);
return copy_to_user(otmr, &kotmr, sizeof(kotmr)) ? -EFAULT: 0;
}
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