linux-kernel - Re: 2.6.21-mm1 hwsusp: BUG at workqueue.c:106

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Date:	Tue, 8 May 2007 18:20:25 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	linux-pm@...ts.linux-foundation.org,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-mm1 hwsusp: BUG at workqueue.c:106

On 05/08, Oleg Nesterov wrote:
>
> On 05/08, Jiri Slaby wrote:
> >
> > vmstat_update+0x0/0x2b
> 
> Thanks a lot.
> 
> Right now,
> 
> > +static void vmstat_update(struct work_struct *w)
> > +{
> > +       refresh_cpu_vm_stats(smp_processor_id());
> > +       schedule_delayed_work(&__get_cpu_var(vmstat_work),
> > +               sysctl_stat_interval);
> > +}
> 
> This is not precisely correct. We cam schedule the wrong vmstat_work
> if this timer/work migrates to another CPU. I'd suggest
> 
> 	schedule_delayed_work(container_of(w, struct delayed_work, work))
> 
> 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.

Oleg.

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