linux-kernel - [PATCH 0/2] validate the delta of cycle_now and cycle

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Message-ID: <1445952073-7260-1-git-send-email-yangyingliang@huawei.com>
Date:	Tue, 27 Oct 2015 21:21:11 +0800
From:	Yang Yingliang <yangyingliang@...wei.com>
To:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
CC:	Yang Yingliang <yangyingliang@...wei.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 0/2] validate the delta of cycle_now and cycle_last on arm64

In multi-core system, if the clock is not sync perfectly, it
will make cycle_last that recorded by CPU-A is a little more
than cycle_now that read by CPU-B. With the negative result,
hrtimer_update_base() return a huge and wrong time. It leads
to the cpu can not finish the while loop in hrtimer_interrupt()
until the real nowtime which is returned from ktime_get() catch
up with the wrong time on clock monotonic base.

Fix it by select config CLOCKSOURCE_VALIDATE_LAST_CYCLE.

Cc: Thomas Gleixner <tglx@...utronix.de>

Yang Yingliang (2):
  clocksource: replace cycle_last validation with an equal way
  arm64: validate the cycle_last to prevent time going backwards

 arch/arm64/Kconfig                 | 1 +
 kernel/time/timekeeping_internal.h | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

-- 
2.5.0

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