linux-kernel - Re: [PATCH]: Fix bogus softlockup warning with sysrq-t

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Message-ID: <4608AF01.4060804@goop.org>
Date:	Mon, 26 Mar 2007 22:43:29 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Prarit Bhargava <prarit@...hat.com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	clalance@...hat.com, mingo@...hat.com, davej@...hat.com,
	Thilo.Cestonaro.external@...itsu-siemens.com
Subject: Re: [PATCH]: Fix bogus softlockup warning with sysrq-t

Prarit Bhargava wrote:
> There are some situations when soft lockup warnings are expected in the
> kernel.  For example, when doing an alt-sysrq-t on a large number of processes,
> the dump to console can take a long time and the tasklist_lock is held over
> that period.  This results in a bogus soft lockup warning.
>   

Wouldn't it be better to just temporarily disable softlockups for the
duration?

> This patch reworks touch_softlockup_watchdog to touch ALL cpu's
> touch_timestamp.  It also introduces touch_cpu_softlockup_watchdog to touch
> a single cpu's touch_timestamp.

Doesn't this mean that if one CPU gets locked up, it will be undetected
so long as some other CPU is making progress?

I have another pair of softlockup patches in which I try to address:

    * ignoring time stolen by hypervisors
    * threads going to sleep tickless for long periods of time

I could easy add a "global disable" function, which would allow long
sysrq messages, and it would help Thilo with his long flash update freezes.

    J
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