linux-kernel - Re: [patch] fix the softlockup watchdog to actually work

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Message-ID: <86802c440710031649n47c9630qf5e8f8fdc569c45e@mail.gmail.com>
Date:	Wed, 3 Oct 2007 16:49:14 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	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] fix the softlockup watchdog to actually work

On 7/17/07, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>
> > 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"?
>
> uhm, the problem was that it did not work _at all_, not something about
> 'rate limiting'. Yes, i got quite a bit grumpy when i found this,
> because you completely broke the softlockup watchdog via a pretty
> intrusive commit and you apparently didnt even do a minimal check
> whether its functionality was preserved! Updated patch for Andrew/Linus
> and for -stable attached.
>
>         Ingo
>
> ----------------------------->
> Subject: fix the softlockup watchdog to actually work
> From: Ingo Molnar <mingo@...e.hu>
>
> this Xen related commit:
>
>    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 in essence 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;
> +       }
>
>         /* do not print during early bootup: */
>         if (unlikely(system_state != SYSTEM_RUNNING)) {
> -

how about

diff --git a/kernel/softlockup.c b/kernel/softlockup.c
index 708d488..bbc0292 100644
--- a/kernel/softlockup.c
+++ b/kernel/softlockup.c
@@ -80,7 +80,7 @@ void softlockup_tick(void)
        print_timestamp = per_cpu(print_timestamp, this_cpu);

        /* report at most once a second */
-       if (print_timestamp < (touch_timestamp + 1) ||
+       if (((touch_timestamp - print_timestamp) < 1) ||
                did_panic ||
                        !per_cpu(watchdog_task, this_cpu))


YH
-
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