linux-kernel - Re: [patch] softlockup watchdog: fix Xen bogosity

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Date:	Tue, 17 Jul 2007 07:17:51 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...nel.org, Greg KH <greg@...ah.com>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [patch] softlockup watchdog: fix Xen bogosity

Ingo Molnar wrote:
> Subject: softlockup: fix Xen bogosity
> From: Ingo Molnar <mingo@...e.hu>
>
> this Xen related commit:
>   

Well, not just Xen.  It relates to any virtual environment: kvm, lguest,
vmi, xen...  (Not that they all implement a measure of unstolen time.)

How about a more descriptive patch title, along the lines of "softlockup
watchdog: fix rate limiting"?

>    commit 966812dc98e6a7fcdf759cbfa0efab77500a8868
>    Author: Jeremy Fitzhardinge <jeremy@...p.org>
>    Date:   Tue May 8 00:28:02 2007 -0700
>
>        Ignore stolen time in the softlockup watchdog
>
> broke the softlockup watchdog to never report any lockups. (!)
>
> print_timestamp defaults to 0, this makes the following condition
> always true:
>
> 	if (print_timestamp < (touch_timestamp + 1) ||
>
> and we'll never report soft lockups.
>
> apparently the functionality of the soft lockup watchdog was never 
> actually tested with that patch applied ...
>
> [ this is -stable material too. ]
>
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> ---
>  kernel/softlockup.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> Index: linux/kernel/softlockup.c
> ===================================================================
> --- linux.orig/kernel/softlockup.c
> +++ linux/kernel/softlockup.c
> @@ -79,10 +79,11 @@ void softlockup_tick(void)
>  	print_timestamp = per_cpu(print_timestamp, this_cpu);
>  
>  	/* report at most once a second */
> -	if (print_timestamp < (touch_timestamp + 1) ||
> -		did_panic ||
> -			!per_cpu(watchdog_task, this_cpu))
> +	if ((print_timestamp >= touch_timestamp &&
> +			print_timestamp < (touch_timestamp + 1)) ||
> +			did_panic || !per_cpu(watchdog_task, this_cpu)) {
>  		return;
> +	}
>   

OK, thanks.

Acked-by: Jeremy Fitzhardinge <jeremy@...source.com>

    J
-
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