linux-kernel - Re: [PATCH 1/1] vmstat-use-our-own-timer-events-fix

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Date:	Tue, 8 May 2007 18:42:24 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] vmstat-use-our-own-timer-events-fix

On 05/08, Jiri Slaby wrote:
>
> Oleg Nesterov wrote:
> > On 05/08, Oleg Nesterov wrote:
> > >
> > > On 05/08, Jiri Slaby wrote:
> > >
> > > This should not happen because we are doing cancel_rearming_delayed_work()
> > > below, however:
> > > 
> > > > +       case CPU_DOWN_PREPARE:
> > > > +       case CPU_DOWN_PREPARE_FROZEN:
> > > > +               cancel_rearming_delayed_work(&per_cpu(vmstat_work, cpu));
> > > > +               per_cpu(vmstat_work, cpu).work.func = NULL;
> > > > +       case CPU_DOWN_FAILED:
> > > > +       case CPU_DOWN_FAILED_FROZEN:
> > > > +               start_cpu_timer(cpu);
> > > 
> > > we need a "break;" before "case CPU_DOWN_FAILED", otherwise we re-start
> > > vmstat_update() immediately.
> > > 
> > > This is a bug, but I am not sure is this the only problem.
> > 
> > In case I was not clear, this _can_ explain the problem. Because an extra
> > start_cpu_timer() (due to missed "break;") re-initializes dwork, and clears
> > _PENDING.
> 
> Yes, it helped, thanks. If no objections, please apply the patch below.

Great! Thanks.

> 
> vmstat-use-our-own-timer-events-fix
> 
> add missing break
> 
> Cc: Christoph Lameter <clameter@....com>
> Cc: Arjan van de Ven <arjan@...ux.intel.com>
> Signed-off-by: Jiri Slaby <jirislaby@...il.com>
> 
> ---
> commit e0fe3cf4776a3c16ac7625ce9eae75ea42eb9b4e
> tree c9a4277860e2cea03911b3d73c9386c9284d991b
> parent b1034323f7e57642eee59a0f5e77c50bc26982c5
> author Jiri Slaby <jirislaby@...il.com> Tue, 08 May 2007 16:25:28 +0200
> committer Jiri Slaby <jirislaby@...il.com> Tue, 08 May 2007 16:25:28 +0200
> 
>  mm/vmstat.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 709e2f0..fac05e8 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -677,6 +677,7 @@ static int __cpuinit vmstat_cpuup_callback(struct notifier_block *nfb,
>  	case CPU_DOWN_PREPARE_FROZEN:
>  		cancel_rearming_delayed_work(&per_cpu(vmstat_work, cpu));
>  		per_cpu(vmstat_work, cpu).work.func = NULL;
> +		break;
>  	case CPU_DOWN_FAILED:
>  	case CPU_DOWN_FAILED_FROZEN:
>  		start_cpu_timer(cpu);

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