linux-kernel - Confusing behaviour with /proc/sys/kernel/nmi

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Message-ID: <20141105093420.1c7500d8@kryten>
Date:	Wed, 5 Nov 2014 09:34:20 +1100
From:	Anton Blanchard <anton@...ba.org>
To:	uobergfe@...hat.com, drjones@...hat.com, dzickus@...hat.com,
	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org
Subject: Confusing behaviour with /proc/sys/kernel/nmi_watchdog

Hi,

commit 9919e39a1738 ("kvm: ensure hard lockup detection is disabled by
default") provided a way for the kernel to disable the hard lockup
detector at runtime.

I'm using it on ppc64 but notice some weird behaviour with the
nmi_watchdog procfs variable. At boot, that the hard lockup
detector appears to be enabled even when we disable it via
watchdog_enable_hardlockup_detector(false):

# cat /proc/sys/kernel/nmi_watchdog 
1

I have to echo 0 to it then echo 1 again to enable it.

Anton
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