![Andreas Sandberg](/assets/img/avatar_default.png)
The hrtimer callback in the hrtimer's tick broadcast code sometimes incorrectly ends up scheduling events at the current tick causing the kernel to hang servicing the same hrtimer forever. This typically happens when a device is swapped out by tick_install_broadcast_device(), which replaces the event handler with clock_events_handle_noop() and sets the device mode to CLOCK_EVT_MODE_UNUSED. If the timer is scheduled when this happens, the next_event field will not be updated and the hrtimer ends up being restarted at the current tick. To prevent this from happening, only try to restart the hrtimer if the broadcast clock event device is in one of the active modes and try to cancel the timer when entering the CLOCK_EVT_MODE_UNUSED mode. Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com> Tested-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/1429880765-5558-1-git-send-email-andreas.sandberg@arm.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
120 lines
3.1 KiB
C
120 lines
3.1 KiB
C
/*
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* linux/kernel/time/tick-broadcast-hrtimer.c
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* This file emulates a local clock event device
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* via a pseudo clock device.
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*/
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#include <linux/cpu.h>
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#include <linux/err.h>
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#include <linux/hrtimer.h>
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#include <linux/interrupt.h>
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#include <linux/percpu.h>
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#include <linux/profile.h>
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#include <linux/clockchips.h>
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#include <linux/sched.h>
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#include <linux/smp.h>
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#include <linux/module.h>
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#include "tick-internal.h"
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static struct hrtimer bctimer;
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static void bc_set_mode(enum clock_event_mode mode,
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struct clock_event_device *bc)
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{
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switch (mode) {
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case CLOCK_EVT_MODE_UNUSED:
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case CLOCK_EVT_MODE_SHUTDOWN:
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/*
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* Note, we cannot cancel the timer here as we might
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* run into the following live lock scenario:
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*
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* cpu 0 cpu1
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* lock(broadcast_lock);
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* hrtimer_interrupt()
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* bc_handler()
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* tick_handle_oneshot_broadcast();
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* lock(broadcast_lock);
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* hrtimer_cancel()
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* wait_for_callback()
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*/
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hrtimer_try_to_cancel(&bctimer);
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break;
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default:
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break;
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}
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}
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/*
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* This is called from the guts of the broadcast code when the cpu
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* which is about to enter idle has the earliest broadcast timer event.
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*/
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static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
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{
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int bc_moved;
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/*
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* We try to cancel the timer first. If the callback is on
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* flight on some other cpu then we let it handle it. If we
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* were able to cancel the timer nothing can rearm it as we
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* own broadcast_lock.
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*
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* However we can also be called from the event handler of
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* ce_broadcast_hrtimer itself when it expires. We cannot
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* restart the timer because we are in the callback, but we
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* can set the expiry time and let the callback return
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* HRTIMER_RESTART.
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*
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* Since we are in the idle loop at this point and because
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* hrtimer_{start/cancel} functions call into tracing,
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* calls to these functions must be bound within RCU_NONIDLE.
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*/
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RCU_NONIDLE({
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bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
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if (bc_moved)
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hrtimer_start(&bctimer, expires,
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HRTIMER_MODE_ABS_PINNED);});
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if (bc_moved) {
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/* Bind the "device" to the cpu */
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bc->bound_on = smp_processor_id();
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} else if (bc->bound_on == smp_processor_id()) {
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hrtimer_set_expires(&bctimer, expires);
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}
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return 0;
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}
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static struct clock_event_device ce_broadcast_hrtimer = {
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.set_mode = bc_set_mode,
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.set_next_ktime = bc_set_next,
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.features = CLOCK_EVT_FEAT_ONESHOT |
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CLOCK_EVT_FEAT_KTIME |
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CLOCK_EVT_FEAT_HRTIMER,
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.rating = 0,
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.bound_on = -1,
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.min_delta_ns = 1,
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.max_delta_ns = KTIME_MAX,
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.min_delta_ticks = 1,
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.max_delta_ticks = ULONG_MAX,
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.mult = 1,
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.shift = 0,
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.cpumask = cpu_all_mask,
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};
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static enum hrtimer_restart bc_handler(struct hrtimer *t)
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{
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ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
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switch (ce_broadcast_hrtimer.mode) {
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case CLOCK_EVT_MODE_ONESHOT:
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if (ce_broadcast_hrtimer.next_event.tv64 != KTIME_MAX)
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return HRTIMER_RESTART;
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default:
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return HRTIMER_NORESTART;
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}
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}
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void tick_setup_hrtimer_broadcast(void)
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{
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hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
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bctimer.function = bc_handler;
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clockevents_register_device(&ce_broadcast_hrtimer);
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}
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