Re: slab: start_cpu_timer/cache_reap CONFIG_HOTPLUG_CPU problems

[Oleg Nesterov <oleg@tv-sign.ru>]

On 01/29, Christoph Lameter wrote:
>
> On Mon, 29 Jan 2007, Oleg Nesterov wrote:
> 
> > >                                      The slab would need a notification 
> > > that the workqueue for a processor was shutdown in order to set work.func 
> > > = NULL.
> > 
> > The slab has a notification: CPU_XXX events. It should cancel a pending per
> > cpu "reap_work timer".
> 
> Ahh. Okay then the following patch would fix it?
> 
> Shutdown cache_reaper when cpu goes down
> 
> Shutdown the cache_reaper in slab.c if the cpu is brought down
> and set the cache_reap.func to NULL. Otherwise hotplug shuts
> down the reaper for good.
> 
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
> Index: linux-2.6.20-rc6/mm/slab.c
> ===================================================================
> --- linux-2.6.20-rc6.orig/mm/slab.c	2007-01-24 20:19:28.000000000 -0600
> +++ linux-2.6.20-rc6/mm/slab.c	2007-01-29 13:08:05.773928988 -0600
> @@ -1269,6 +1269,10 @@ static int __cpuinit cpuup_callback(stru
>  		break;
>  #ifdef CONFIG_HOTPLUG_CPU
>  	case CPU_DOWN_PREPARE:
> +		/* Shutdown cache reaper */
> +		cancel_rearming_delayed_work(&per_cpu(reap_work, cpu));
> +		per_cpu(reap_work, cpu).work.func = NULL;
> +
>  		mutex_lock(&cache_chain_mutex);
>  		break;
>  	case CPU_DOWN_FAILED:

Then CPU_DOWN_FAILED should do start_cpu_timer(cpu).

Oleg.