linux-kernel - Re: [rfc/patch] mm/slub: restore/expand unfreeze

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Date:   Fri, 09 Jul 2021 21:28:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mike Galbraith <efault@....de>, LKML <linux-kernel@...r.kernel.org>
Cc:     linux-rt-users@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [rfc/patch] mm/slub: restore/expand unfreeze_partials() local exclusion scope

On Fri, Jul 09 2021 at 07:21, Mike Galbraith wrote:
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2497,7 +2497,9 @@ static void put_cpu_partial(struct kmem_
>  				 * partial array is full. Move the existing
>  				 * set to the per node partial list.
>  				 */
> +				local_lock(&s->cpu_slab->lock);
>  				unfreeze_partials(s);
> +				local_unlock(&s->cpu_slab->lock);
>  				oldpage = NULL;
>  				pobjects = 0;
>  				pages = 0;
> @@ -2579,7 +2581,9 @@ static void flush_cpu_slab(struct work_s
>  	if (c->page)
>  		flush_slab(s, c, true);
>  
> +	local_lock(&s->cpu_slab->lock);
>  	unfreeze_partials(s);
> +	local_unlock(&s->cpu_slab->lock);
>  }
>  
>  static bool has_cpu_slab(int cpu, struct kmem_cache *s)
> @@ -2632,8 +2636,11 @@ static int slub_cpu_dead(unsigned int cp
>  	struct kmem_cache *s;
>  
>  	mutex_lock(&slab_mutex);
> -	list_for_each_entry(s, &slab_caches, list)
> +	list_for_each_entry(s, &slab_caches, list) {
> +		local_lock(&s->cpu_slab->lock);

This one is odd. It locks the cpu_slab lock of the CPU which runs this
callback and then flushes the slab of the dead CPU.

Thanks,

        tglx