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![Linus Torvalds](/assets/img/avatar_default.png)
The poll() changes were not well thought out, and completely unexplained. They also caused a huge performance regression, because "->poll()" was no longer a trivial file operation that just called down to the underlying file operations, but instead did at least two indirect calls. Indirect calls are sadly slow now with the Spectre mitigation, but the performance problem could at least be largely mitigated by changing the "->get_poll_head()" operation to just have a per-file-descriptor pointer to the poll head instead. That gets rid of one of the new indirections. But that doesn't fix the new complexity that is completely unwarranted for the regular case. The (undocumented) reason for the poll() changes was some alleged AIO poll race fixing, but we don't make the common case slower and more complex for some uncommon special case, so this all really needs way more explanations and most likely a fundamental redesign. [ This revert is a revert of about 30 different commits, not reverted individually because that would just be unnecessarily messy - Linus ] Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
589 lines
13 KiB
C
589 lines
13 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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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/alarmtimer.h>
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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/compat.h>
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#include <linux/rcupdate.h>
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struct timerfd_ctx {
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union {
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struct hrtimer tmr;
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struct alarm alarm;
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} t;
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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 clockid;
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short unsigned expired;
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short unsigned settime_flags; /* to show in fdinfo */
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struct rcu_head rcu;
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struct list_head clist;
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spinlock_t cancel_lock;
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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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static inline bool isalarm(struct timerfd_ctx *ctx)
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{
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return ctx->clockid == CLOCK_REALTIME_ALARM ||
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ctx->clockid == CLOCK_BOOTTIME_ALARM;
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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 != 0) until the timer is accessed.
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*/
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static void timerfd_triggered(struct timerfd_ctx *ctx)
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{
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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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}
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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,
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t.tmr);
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timerfd_triggered(ctx);
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return HRTIMER_NORESTART;
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}
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static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
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ktime_t now)
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{
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struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
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t.alarm);
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timerfd_triggered(ctx);
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return ALARMTIMER_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_mono_to_real(0);
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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 != moffs) {
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ctx->moffs = 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 void timerfd_remove_cancel(struct timerfd_ctx *ctx)
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{
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spin_lock(&ctx->cancel_lock);
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__timerfd_remove_cancel(ctx);
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spin_unlock(&ctx->cancel_lock);
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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 != KTIME_MAX)
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return false;
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ctx->moffs = ktime_mono_to_real(0);
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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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spin_lock(&ctx->cancel_lock);
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if ((ctx->clockid == CLOCK_REALTIME ||
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ctx->clockid == CLOCK_REALTIME_ALARM) &&
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(flags & TFD_TIMER_ABSTIME) && (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 {
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__timerfd_remove_cancel(ctx);
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}
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spin_unlock(&ctx->cancel_lock);
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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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if (isalarm(ctx))
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remaining = alarm_expires_remaining(&ctx->t.alarm);
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else
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remaining = hrtimer_expires_remaining_adjusted(&ctx->t.tmr);
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return remaining < 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 itimerspec64 *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 = timespec64_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 = timespec64_to_ktime(ktmr->it_interval);
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if (isalarm(ctx)) {
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alarm_init(&ctx->t.alarm,
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ctx->clockid == CLOCK_REALTIME_ALARM ?
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ALARM_REALTIME : ALARM_BOOTTIME,
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timerfd_alarmproc);
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} else {
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hrtimer_init(&ctx->t.tmr, clockid, htmode);
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hrtimer_set_expires(&ctx->t.tmr, texp);
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ctx->t.tmr.function = timerfd_tmrproc;
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}
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if (texp != 0) {
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if (isalarm(ctx)) {
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if (flags & TFD_TIMER_ABSTIME)
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alarm_start(&ctx->t.alarm, texp);
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else
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alarm_start_relative(&ctx->t.alarm, texp);
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} else {
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hrtimer_start(&ctx->t.tmr, texp, htmode);
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}
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if (timerfd_canceled(ctx))
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return -ECANCELED;
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}
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ctx->settime_flags = flags & TFD_SETTIME_FLAGS;
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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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if (isalarm(ctx))
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alarm_cancel(&ctx->t.alarm);
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else
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hrtimer_cancel(&ctx->t.tmr);
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kfree_rcu(ctx, rcu);
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return 0;
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}
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static __poll_t 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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__poll_t 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 |= EPOLLIN;
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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) {
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/*
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* If tintv != 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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if (isalarm(ctx)) {
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ticks += alarm_forward_now(
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&ctx->t.alarm, ctx->tintv) - 1;
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alarm_restart(&ctx->t.alarm);
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} else {
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ticks += hrtimer_forward_now(&ctx->t.tmr,
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ctx->tintv) - 1;
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hrtimer_restart(&ctx->t.tmr);
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}
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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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#ifdef CONFIG_PROC_FS
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static void timerfd_show(struct seq_file *m, struct file *file)
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{
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struct timerfd_ctx *ctx = file->private_data;
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struct itimerspec t;
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spin_lock_irq(&ctx->wqh.lock);
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t.it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
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t.it_interval = ktime_to_timespec(ctx->tintv);
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spin_unlock_irq(&ctx->wqh.lock);
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seq_printf(m,
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"clockid: %d\n"
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"ticks: %llu\n"
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"settime flags: 0%o\n"
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"it_value: (%llu, %llu)\n"
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"it_interval: (%llu, %llu)\n",
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ctx->clockid,
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(unsigned long long)ctx->ticks,
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ctx->settime_flags,
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(unsigned long long)t.it_value.tv_sec,
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(unsigned long long)t.it_value.tv_nsec,
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(unsigned long long)t.it_interval.tv_sec,
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(unsigned long long)t.it_interval.tv_nsec);
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}
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#else
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#define timerfd_show NULL
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#endif
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#ifdef CONFIG_CHECKPOINT_RESTORE
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static long timerfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
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{
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struct timerfd_ctx *ctx = file->private_data;
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int ret = 0;
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switch (cmd) {
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case TFD_IOC_SET_TICKS: {
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u64 ticks;
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if (copy_from_user(&ticks, (u64 __user *)arg, sizeof(ticks)))
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return -EFAULT;
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if (!ticks)
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return -EINVAL;
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spin_lock_irq(&ctx->wqh.lock);
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if (!timerfd_canceled(ctx)) {
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ctx->ticks = ticks;
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wake_up_locked(&ctx->wqh);
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} else
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ret = -ECANCELED;
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spin_unlock_irq(&ctx->wqh.lock);
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break;
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}
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default:
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ret = -ENOTTY;
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break;
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}
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return ret;
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}
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#else
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#define timerfd_ioctl NULL
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#endif
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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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.show_fdinfo = timerfd_show,
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.unlocked_ioctl = timerfd_ioctl,
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};
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static int timerfd_fget(int fd, struct fd *p)
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{
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struct fd f = fdget(fd);
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if (!f.file)
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return -EBADF;
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if (f.file->f_op != &timerfd_fops) {
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fdput(f);
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return -EINVAL;
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}
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*p = f;
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return 0;
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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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clockid != CLOCK_REALTIME_ALARM &&
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clockid != CLOCK_BOOTTIME &&
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clockid != CLOCK_BOOTTIME_ALARM))
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return -EINVAL;
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if ((clockid == CLOCK_REALTIME_ALARM ||
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clockid == CLOCK_BOOTTIME_ALARM) &&
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!capable(CAP_WAKE_ALARM))
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return -EPERM;
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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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spin_lock_init(&ctx->cancel_lock);
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ctx->clockid = clockid;
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if (isalarm(ctx))
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alarm_init(&ctx->t.alarm,
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ctx->clockid == CLOCK_REALTIME_ALARM ?
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ALARM_REALTIME : ALARM_BOOTTIME,
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timerfd_alarmproc);
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else
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hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
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ctx->moffs = ktime_mono_to_real(0);
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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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static int do_timerfd_settime(int ufd, int flags,
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const struct itimerspec64 *new,
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struct itimerspec64 *old)
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{
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struct fd f;
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struct timerfd_ctx *ctx;
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int ret;
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if ((flags & ~TFD_SETTIME_FLAGS) ||
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!itimerspec64_valid(new))
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return -EINVAL;
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ret = timerfd_fget(ufd, &f);
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if (ret)
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return ret;
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ctx = f.file->private_data;
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if (isalarm(ctx) && !capable(CAP_WAKE_ALARM)) {
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fdput(f);
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return -EPERM;
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}
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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 (isalarm(ctx)) {
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if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
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break;
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} else {
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if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
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break;
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}
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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) {
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if (isalarm(ctx))
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alarm_forward_now(&ctx->t.alarm, ctx->tintv);
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else
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hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
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}
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old->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
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old->it_interval = ktime_to_timespec64(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, new);
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spin_unlock_irq(&ctx->wqh.lock);
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fdput(f);
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return ret;
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}
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static int do_timerfd_gettime(int ufd, struct itimerspec64 *t)
|
|
{
|
|
struct fd f;
|
|
struct timerfd_ctx *ctx;
|
|
int ret = timerfd_fget(ufd, &f);
|
|
if (ret)
|
|
return ret;
|
|
ctx = f.file->private_data;
|
|
|
|
spin_lock_irq(&ctx->wqh.lock);
|
|
if (ctx->expired && ctx->tintv) {
|
|
ctx->expired = 0;
|
|
|
|
if (isalarm(ctx)) {
|
|
ctx->ticks +=
|
|
alarm_forward_now(
|
|
&ctx->t.alarm, ctx->tintv) - 1;
|
|
alarm_restart(&ctx->t.alarm);
|
|
} else {
|
|
ctx->ticks +=
|
|
hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
|
|
- 1;
|
|
hrtimer_restart(&ctx->t.tmr);
|
|
}
|
|
}
|
|
t->it_value = ktime_to_timespec64(timerfd_get_remaining(ctx));
|
|
t->it_interval = ktime_to_timespec64(ctx->tintv);
|
|
spin_unlock_irq(&ctx->wqh.lock);
|
|
fdput(f);
|
|
return 0;
|
|
}
|
|
|
|
SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
|
|
const struct itimerspec __user *, utmr,
|
|
struct itimerspec __user *, otmr)
|
|
{
|
|
struct itimerspec64 new, old;
|
|
int ret;
|
|
|
|
if (get_itimerspec64(&new, utmr))
|
|
return -EFAULT;
|
|
ret = do_timerfd_settime(ufd, flags, &new, &old);
|
|
if (ret)
|
|
return ret;
|
|
if (otmr && put_itimerspec64(&old, otmr))
|
|
return -EFAULT;
|
|
|
|
return ret;
|
|
}
|
|
|
|
SYSCALL_DEFINE2(timerfd_gettime, int, ufd, struct itimerspec __user *, otmr)
|
|
{
|
|
struct itimerspec64 kotmr;
|
|
int ret = do_timerfd_gettime(ufd, &kotmr);
|
|
if (ret)
|
|
return ret;
|
|
return put_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
|
|
}
|
|
|
|
#ifdef CONFIG_COMPAT
|
|
COMPAT_SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags,
|
|
const struct compat_itimerspec __user *, utmr,
|
|
struct compat_itimerspec __user *, otmr)
|
|
{
|
|
struct itimerspec64 new, old;
|
|
int ret;
|
|
|
|
if (get_compat_itimerspec64(&new, utmr))
|
|
return -EFAULT;
|
|
ret = do_timerfd_settime(ufd, flags, &new, &old);
|
|
if (ret)
|
|
return ret;
|
|
if (otmr && put_compat_itimerspec64(&old, otmr))
|
|
return -EFAULT;
|
|
return ret;
|
|
}
|
|
|
|
COMPAT_SYSCALL_DEFINE2(timerfd_gettime, int, ufd,
|
|
struct compat_itimerspec __user *, otmr)
|
|
{
|
|
struct itimerspec64 kotmr;
|
|
int ret = do_timerfd_gettime(ufd, &kotmr);
|
|
if (ret)
|
|
return ret;
|
|
return put_compat_itimerspec64(&kotmr, otmr) ? -EFAULT : 0;
|
|
}
|
|
#endif
|