linux-kernel - [28/80] hrtimer: Fix extra wakeups from __remove

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Date:	Wed, 07 Dec 2011 08:06:48 -0800
From:	Greg KH <gregkh@...e.de>
To:	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Cc:	<torvalds@...ux-foundation.org>, <akpm@...ux-foundation.org>,
	<alan@...rguk.ukuu.org.uk>,
	Jeff Ohlstein <johlstei@...eaurora.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [28/80] hrtimer: Fix extra wakeups from __remove_hrtimer()

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jeff Ohlstein <johlstei@...eaurora.org>

commit 27c9cd7e601632b3794e1c3344d37b86917ffb43 upstream.

__remove_hrtimer() attempts to reprogram the clockevent device when
the timer being removed is the next to expire. However,
__remove_hrtimer() reprograms the clockevent *before* removing the
timer from the timerqueue and thus when hrtimer_force_reprogram()
finds the next timer to expire it finds the timer we're trying to
remove.

This is especially noticeable when the system switches to NOHz mode
and the system tick is removed. The timer tick is removed from the
system but the clockevent is programmed to wakeup in another HZ
anyway.

Silence the extra wakeup by removing the timer from the timerqueue
before calling hrtimer_force_reprogram() so that we actually program
the clockevent for the next timer to expire.

This was broken by 998adc3 "hrtimers: Convert hrtimers to use
timerlist infrastructure".

Signed-off-by: Jeff Ohlstein <johlstei@...eaurora.org>
Link: http://lkml.kernel.org/r/1321660030-8520-1-git-send-email-johlstei@codeaurora.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/hrtimer.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -885,10 +885,13 @@ static void __remove_hrtimer(struct hrti
 			     struct hrtimer_clock_base *base,
 			     unsigned long newstate, int reprogram)
 {
+	struct timerqueue_node *next_timer;
 	if (!(timer->state & HRTIMER_STATE_ENQUEUED))
 		goto out;

-	if (&timer->node == timerqueue_getnext(&base->active)) {
+	next_timer = timerqueue_getnext(&base->active);
+	timerqueue_del(&base->active, &timer->node);
+	if (&timer->node == next_timer) {
 #ifdef CONFIG_HIGH_RES_TIMERS
 		/* Reprogram the clock event device. if enabled */
 		if (reprogram && hrtimer_hres_active()) {
@@ -901,7 +904,6 @@ static void __remove_hrtimer(struct hrti
 		}
 #endif
 	}
-	timerqueue_del(&base->active, &timer->node);
 	if (!timerqueue_getnext(&base->active))
 		base->cpu_base->active_bases &= ~(1 << base->index);
 out:

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