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Commit 9ec26907 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

timerfd: Manage cancelable timers in timerfd 



Peter is concerned about the extra scan of CLOCK_REALTIME_COS in the
timer interrupt. Yes, I did not think about it, because the solution
was so elegant. I didn't like the extra list in timerfd when it was
proposed some time ago, but with a rcu based list the list walk it's
less horrible than the original global lock, which was held over the
list iteration.

Requested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarPeter Zijlstra <peterz@infradead.org>
parent 250f972d

fs/timerfd.c

+74 −31
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <linux/anon_inodes.h>

#include <linux/timerfd.h>

#include <linux/syscalls.h>

#include <linux/rcupdate.h>



struct timerfd_ctx {

	struct hrtimer tmr;
@@ -31,9 +32,14 @@ struct timerfd_ctx { 
	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,
@@ -53,28 +59,69 @@ static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr) 
	return HRTIMER_NORESTART;

}



static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)

/*

 * Called when the clock was set to cancel the timers in the cancel

 * list.

 */

void timerfd_clock_was_set(void)

{

	ktime_t remaining;

	ktime_t moffs = ktime_get_monotonic_offset();

	struct timerfd_ctx *ctx;

	unsigned long flags;



	remaining = hrtimer_expires_remaining(&ctx->tmr);

	return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;

	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;

			wake_up_locked(&ctx->wqh);

		}

		spin_unlock_irqrestore(&ctx->wqh.lock, flags);

	}

	rcu_read_unlock();

}



static bool timerfd_canceled(struct timerfd_ctx *ctx)

static void timerfd_remove_cancel(struct timerfd_ctx *ctx)

{

	ktime_t moffs;

	if (ctx->might_cancel) {

		ctx->might_cancel = false;

		spin_lock(&cancel_lock);

		list_del_rcu(&ctx->clist);

		spin_unlock(&cancel_lock);

	}

}



	if (!ctx->might_cancel)

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;

}



	moffs = ktime_get_monotonic_offset();

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);

	}

}



	if (moffs.tv64 == ctx->moffs.tv64)

		return false;

static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)

{

	ktime_t remaining;



	ctx->moffs = moffs;

	return true;

	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,
@@ -87,13 +134,6 @@ static int timerfd_setup(struct timerfd_ctx *ctx, int flags, 
	htmode = (flags & TFD_TIMER_ABSTIME) ?

		HRTIMER_MODE_ABS: HRTIMER_MODE_REL;



	ctx->might_cancel = false;

	if (htmode == HRTIMER_MODE_ABS && ctx->clockid == CLOCK_REALTIME &&

	    (flags & TFD_TIMER_CANCELON_SET)) {

		clockid = CLOCK_REALTIME_COS;

		ctx->might_cancel = true;

	}



	texp = timespec_to_ktime(ktmr->it_value);

	ctx->expired = 0;

	ctx->ticks = 0;
@@ -113,8 +153,9 @@ 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(ctx);

	kfree_rcu(ctx, rcu);

	return 0;

}
@@ -149,20 +190,20 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count, 
	else

		res = wait_event_interruptible_locked_irq(ctx->wqh, ctx->ticks);



	if (ctx->ticks) {

		ticks = 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)) {

			ticks = 0;

		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
@@ -258,6 +299,8 @@ SYSCALL_DEFINE4(timerfd_settime, int, ufd, int, flags, 
		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.

include/linux/hrtimer.h

+5 −1
Original line number Diff line number Diff line
@@ -155,7 +155,6 @@ enum hrtimer_base_type { 
	HRTIMER_BASE_REALTIME,

	HRTIMER_BASE_MONOTONIC,

	HRTIMER_BASE_BOOTTIME,

	HRTIMER_BASE_REALTIME_COS,

	HRTIMER_MAX_CLOCK_BASES,

};
@@ -306,6 +305,11 @@ static inline int hrtimer_is_hres_active(struct hrtimer *timer) 
#endif



extern void clock_was_set(void);

#ifdef CONFIG_TIMERFD

extern void timerfd_clock_was_set(void);

#else

static inline void timerfd_clock_was_set(void) { }

#endif

extern void hrtimers_resume(void);



extern ktime_t ktime_get(void);

include/linux/time.h

+0 −6
Original line number Diff line number Diff line
@@ -302,12 +302,6 @@ struct itimerval { 
 * The IDs of various hardware clocks:

 */

#define CLOCK_SGI_CYCLE			10



#ifdef __KERNEL__

/* This clock is not exposed to user space */

#define CLOCK_REALTIME_COS		15

#endif



#define MAX_CLOCKS			16

#define CLOCKS_MASK			(CLOCK_REALTIME | CLOCK_MONOTONIC)

#define CLOCKS_MONO			CLOCK_MONOTONIC

include/linux/timerfd.h

+2 −2
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ 
 * shared O_* flags.

 */

#define TFD_TIMER_ABSTIME (1 << 0)

#define TFD_TIMER_CANCELON_SET (1 << 1)

#define TFD_TIMER_CANCEL_ON_SET (1 << 1)

#define TFD_CLOEXEC O_CLOEXEC

#define TFD_NONBLOCK O_NONBLOCK
@@ -27,6 +27,6 @@ 
/* Flags for timerfd_create.  */

#define TFD_CREATE_FLAGS TFD_SHARED_FCNTL_FLAGS

/* Flags for timerfd_settime.  */

#define TFD_SETTIME_FLAGS (TFD_TIMER_ABSTIME | TFD_TIMER_CANCELON_SET)

#define TFD_SETTIME_FLAGS (TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET)



#endif /* _LINUX_TIMERFD_H */

kernel/hrtimer.c

+32 −62
Original line number Diff line number Diff line
@@ -78,11 +78,6 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) = 
			.get_time = &ktime_get_boottime,

			.resolution = KTIME_LOW_RES,

		},

		{

			.index = CLOCK_REALTIME_COS,

			.get_time = &ktime_get_real,

			.resolution = KTIME_LOW_RES,

		},

	}

};
@@ -90,7 +85,6 @@ static const int hrtimer_clock_to_base_table[MAX_CLOCKS] = { 
	[CLOCK_REALTIME]	= HRTIMER_BASE_REALTIME,

	[CLOCK_MONOTONIC]	= HRTIMER_BASE_MONOTONIC,

	[CLOCK_BOOTTIME]	= HRTIMER_BASE_BOOTTIME,

	[CLOCK_REALTIME_COS]	= HRTIMER_BASE_REALTIME_COS,

};



static inline int hrtimer_clockid_to_base(clockid_t clock_id)
@@ -116,7 +110,6 @@ static void hrtimer_get_softirq_time(struct hrtimer_cpu_base *base) 
	base->clock_base[HRTIMER_BASE_REALTIME].softirq_time = xtim;

	base->clock_base[HRTIMER_BASE_MONOTONIC].softirq_time = mono;

	base->clock_base[HRTIMER_BASE_BOOTTIME].softirq_time = boot;

	base->clock_base[HRTIMER_BASE_REALTIME_COS].softirq_time = xtim;

}



/*
@@ -486,8 +479,6 @@ static inline void debug_deactivate(struct hrtimer *timer) 
	trace_hrtimer_cancel(timer);

}



static void hrtimer_expire_cancelable(struct hrtimer_cpu_base *cpu_base);



/* High resolution timer related functions */

#ifdef CONFIG_HIGH_RES_TIMERS
@@ -663,7 +654,33 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer, 
	return 0;

}



static void retrigger_next_event(void *arg);

/*

 * Retrigger next event is called after clock was set

 *

 * Called with interrupts disabled via on_each_cpu()

 */

static void retrigger_next_event(void *arg)

{

	struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);

	struct timespec realtime_offset, xtim, wtm, sleep;



	if (!hrtimer_hres_active())

		return;



	/* Optimized out for !HIGH_RES */

	get_xtime_and_monotonic_and_sleep_offset(&xtim, &wtm, &sleep);

	set_normalized_timespec(&realtime_offset, -wtm.tv_sec, -wtm.tv_nsec);



	/* Adjust CLOCK_REALTIME offset */

	raw_spin_lock(&base->lock);

	base->clock_base[HRTIMER_BASE_REALTIME].offset =

		timespec_to_ktime(realtime_offset);

	base->clock_base[HRTIMER_BASE_BOOTTIME].offset =

		timespec_to_ktime(sleep);



	hrtimer_force_reprogram(base, 0);

	raw_spin_unlock(&base->lock);

}



/*

 * Switch to high resolution mode
@@ -711,45 +728,10 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer, 
	return 0;

}

static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }

static inline void retrigger_next_event(void *arg) { }



#endif /* CONFIG_HIGH_RES_TIMERS */



/*

 * Retrigger next event is called after clock was set

 *

 * Called with interrupts disabled via on_each_cpu()

 */

static void retrigger_next_event(void *arg)

{

	struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);

	struct timespec realtime_offset, xtim, wtm, sleep;



	if (!hrtimer_hres_active()) {

		raw_spin_lock(&base->lock);

		hrtimer_expire_cancelable(base);

		raw_spin_unlock(&base->lock);

		return;

	}



	/* Optimized out for !HIGH_RES */

	get_xtime_and_monotonic_and_sleep_offset(&xtim, &wtm, &sleep);

	set_normalized_timespec(&realtime_offset, -wtm.tv_sec, -wtm.tv_nsec);



	/* Adjust CLOCK_REALTIME offset */

	raw_spin_lock(&base->lock);

	base->clock_base[HRTIMER_BASE_REALTIME].offset =

		timespec_to_ktime(realtime_offset);

	base->clock_base[HRTIMER_BASE_BOOTTIME].offset =

		timespec_to_ktime(sleep);

	base->clock_base[HRTIMER_BASE_REALTIME_COS].offset =

		timespec_to_ktime(realtime_offset);



	hrtimer_expire_cancelable(base);



	hrtimer_force_reprogram(base, 0);

	raw_spin_unlock(&base->lock);

}



/*

 * Clock realtime was set

 *
@@ -763,8 +745,11 @@ static void retrigger_next_event(void *arg) 
 */

void clock_was_set(void)

{

#ifdef CONFIG_HIGHRES_TIMERS

	/* Retrigger the CPU local events everywhere */

	on_each_cpu(retrigger_next_event, NULL, 1);

#endif

	timerfd_clock_was_set();

}



/*
@@ -777,6 +762,7 @@ void hrtimers_resume(void) 
		  KERN_INFO "hrtimers_resume() called with IRQs enabled!");



	retrigger_next_event(NULL);

	timerfd_clock_was_set();

}



static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)
@@ -1240,22 +1226,6 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now) 
	timer->state &= ~HRTIMER_STATE_CALLBACK;

}



static void hrtimer_expire_cancelable(struct hrtimer_cpu_base *cpu_base)

{

	struct timerqueue_node *node;

	struct hrtimer_clock_base *base;

	ktime_t now = ktime_get_real();



	base = &cpu_base->clock_base[HRTIMER_BASE_REALTIME_COS];



	while ((node = timerqueue_getnext(&base->active))) {

			struct hrtimer *timer;



			timer = container_of(node, struct hrtimer, node);

			__run_hrtimer(timer, &now);

	}

}



#ifdef CONFIG_HIGH_RES_TIMERS



/*