linux-kernel - Re: [PATCH] highres: Do not run the TIMER_SOFTIRQ after switching to highres mode

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Date:	Mon, 05 Mar 2007 02:50:22 -0500
From:	Andres Salomon <dilinger@...ian.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] highres: Do not run the TIMER_SOFTIRQ after switching
 to	highres mode

Ingo Molnar wrote:
> * Andres Salomon <dilinger@...ian.org> wrote:
> 
>> Thomas Gleixner wrote:
>>>>> The question is, how the tick timer gets enqueued in the softirq queue.
>>>>> Can you isolate the codepath, where this happens ?
>>> The TIMER_SOFTIRQ runs the hrtimers during bootup until a usable
>>> clocksource and clock event sources are registered. The switch to high
>>> resolution mode happens inside of the TIMER_SOFTIRQ, but runs the
>>> softirq afterwards. That way the tick emulation timer, which was set up
>>> in the switch to highres might be executed in the softirq context, which
>>> is a BUG. The rbtree has not to be touched by the softirq after the
>>> highres switch.
>>>
>> And an additional request, just to make it explicit that we should not 
>> have any NO_SOFTIRQ callbacks in the tree; BUG out if we encounter 
>> such a thing.
> 
> please change it to WARN_ON_ONCE()...
> 
> 'bug out' might mean: 'dead box'/'no resume'/'no bootup'.
> 
> 	Ingo


Certainly; note that hrtimers.c has quite a few BUG calls which could
render a box dead, though.

Patch to follow..

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