Attachment 603554 Details for Bug 836803 – RHEL PATCH 6/7

[patch] RHEL PATCH 6/7

0006-hrtimer-Update-hrtimer-base-offsets-each-hrtimer_int.patch (text/plain), 4.49 KB, created by Prarit Bhargava on 2012-08-10 13:57:10 UTC

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Creator: Prarit Bhargava

Created: 2012-08-10 13:57:10 UTC

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patch

obsolete

>From 0f44cea53697556b098a9c530dbbcde20b97d0f8 Mon Sep 17 00:00:00 2001
>From: Prarit Bhargava <prarit@redhat.com>
>Date: Tue, 24 Jul 2012 10:27:19 -0400
>Subject: hrtimer: Update hrtimer base offsets each hrtimer_interrupt
>
>commit 5baefd6d84163443215f4a99f6a20f054ef11236
>Author: John Stultz <johnstul@us.ibm.com>
>Date:   Tue Jul 10 18:43:25 2012 -0400
>
>    hrtimer: Update hrtimer base offsets each hrtimer_interrupt
>
>    The update of the hrtimer base offsets on all cpus cannot be made
>    atomically from the timekeeper.lock held and interrupt disabled region
>    as smp function calls are not allowed there.
>
>    clock_was_set(), which enforces the update on all cpus, is called
>    either from preemptible process context in case of do_settimeofday()
>    or from the softirq context when the offset modification happened in
>    the timer interrupt itself due to a leap second.
>
>    In both cases there is a race window for an hrtimer interrupt between
>    dropping timekeeper lock, enabling interrupts and clock_was_set()
>    issuing the updates. Any interrupt which arrives in that window will
>    see the new time but operate on stale offsets.
>
>    So we need to make sure that an hrtimer interrupt always sees a
>    consistent state of time and offsets.
>
>    ktime_get_update_offsets() allows us to get the current monotonic time
>    and update the per cpu hrtimer base offsets from hrtimer_interrupt()
>    to capture a consistent state of monotonic time and the offsets. The
>    function replaces the existing ktime_get() calls in hrtimer_interrupt().
>
>    The overhead of the new function vs. ktime_get() is minimal as it just
>    adds two store operations.
>
>    This ensures that any changes to realtime or boottime offsets are
>    noticed and stored into the per-cpu hrtimer base structures, prior to
>    any hrtimer expiration and guarantees that timers are not expired early.
>
>    Signed-off-by: John Stultz <johnstul@us.ibm.com>
>    Reviewed-by: Ingo Molnar <mingo@kernel.org>
>    Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
>    Acked-by: Prarit Bhargava <prarit@redhat.com>
>    Cc: stable@vger.kernel.org
>    Link: http://lkml.kernel.org/r/1341960205-56738-8-git-send-email-johnstul@us.ibm.com
>    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>---
> kernel/hrtimer.c |   27 +++++++++++++--------------
> 1 file changed, 13 insertions(+), 14 deletions(-)
>
>diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
>index 87bb8a5..56ebe16 100644
>--- a/kernel/hrtimer.c
>+++ b/kernel/hrtimer.c
>@@ -662,13 +662,19 @@ static int hrtimer_switch_to_hres(void)
> 	base->clock_base[CLOCK_MONOTONIC].resolution = KTIME_HIGH_RES;
> 
> 	tick_setup_sched_timer();
>-
> 	/* "Retrigger" the interrupt to get things going */
> 	retrigger_next_event(NULL);
> 	local_irq_restore(flags);
> 	return 1;
> }
> 
>+static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base)
>+{
>+	ktime_t *offs_real = &base->clock_base[CLOCK_REALTIME].offset;
>+
>+	return ktime_get_update_offsets(offs_real);
>+}
>+
> /*
>  * Called from timekeeping code to reprogramm the hrtimer interrupt
>  * device. If called from the timer interrupt context we defer it to
>@@ -708,22 +714,12 @@ static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { }
> static void retrigger_next_event(void *arg)
> {
> 	struct hrtimer_cpu_base *base = &__get_cpu_var(hrtimer_bases);
>-	struct timespec realtime_offset, wtm, sleep;
> 
> 	if (!hrtimer_hres_active())
> 		return;
> 
>-	get_xtime_and_monotonic_and_sleep_offset(&realtime_offset, &wtm,
>-							&sleep);
>-	set_normalized_timespec(&realtime_offset, -wtm.tv_sec, -wtm.tv_nsec);
>-
>-	base = &__get_cpu_var(hrtimer_bases);
>-
>-	/* Adjust CLOCK_REALTIME offset */
> 	spin_lock(&base->lock);
>-	base->clock_base[CLOCK_REALTIME].offset =
>-		timespec_to_ktime(realtime_offset);
>-
>+	hrtimer_update_base(base);
> 	hrtimer_force_reprogram(base, 0);
> 	spin_unlock(&base->lock);
> }
>@@ -1245,7 +1241,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
> 	dev->next_event.tv64 = KTIME_MAX;
> 
> 	spin_lock(&cpu_base->lock);
>-	entry_time = now = ktime_get();
>+	entry_time = now = hrtimer_update_base(cpu_base);
> retry:
> 	expires_next.tv64 = KTIME_MAX;
> 	/*
>@@ -1321,9 +1317,12 @@ retry:
> 	 * We need to prevent that we loop forever in the hrtimer
> 	 * interrupt routine. We give it 3 attempts to avoid
> 	 * overreacting on some spurious event.
>+	 *
>+	 * Acquire base lock for updating the offsets and retrieving
>+	 * the current time.
> 	 */
> 	spin_lock(&cpu_base->lock);
>-	now = ktime_get();
>+	now = hrtimer_update_base(cpu_base);
> 	cpu_base->nr_retries++;
> 	if (++retries < 3)
> 		goto retry;
>-- 
>1.7.9.3
>

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