linux-kernel - Re: [PATCH] x86/mce: timer must be setup unconditionally

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Message-Id: <4B1638FE0200007800022FC2@vpn.id2.novell.com>
Date:	Wed, 02 Dec 2009 08:53:02 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Hidetoshi Seto" <seto.hidetoshi@...fujitsu.com>
Cc:	<mingo@...e.hu>, <stable@...nel.org>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: Re: [PATCH] x86/mce: timer must be setup unconditionally

>>> Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> 02.12.09 09:47 >>>
>Jan Beulich wrote:
>> mce_timer must be passed to setup_timer() in all cases, no matter
>> whether it is going to be actually used. Otherwise, when the CPU gets
>> brought down, its call to del_timer_sync() will never return, as the
>> timer won't have a base associated, and hence lock_timer_base() will
>> loop infinitely.
>
>No, what we need to fix is hotplug callbacks.
>So correct fix should be like "del/add timer conditionally when hotplug."

Why? This makes the logic just more complicated (you'd need to track
whether the timer was ever setup or added), and I can't see any
non-tolerable side effect of calling setup_timer() without ever adding
the timer anywhere.

Jan

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