linux-kernel - Re: [PATCH 3/3] mm/slab: use list_{empty_careful,last_entry} in drain

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Message-ID: <alpine.DEB.2.20.1512021005120.28955@east.gentwo.org>
Date:	Wed, 2 Dec 2015 10:06:13 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Geliang Tang <geliangtang@....com>
cc:	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm/slab: use list_{empty_careful,last_entry} in
 drain_freelist

On Wed, 2 Dec 2015, Geliang Tang wrote:

> diff --git a/mm/slab.c b/mm/slab.c
> index 5d5aa3b..1a7d91c 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2362,21 +2362,14 @@ static void drain_cpu_caches(struct kmem_cache *cachep)
>  static int drain_freelist(struct kmem_cache *cache,
>  			struct kmem_cache_node *n, int tofree)
>  {
> -	struct list_head *p;
>  	int nr_freed;
>  	struct page *page;
>
>  	nr_freed = 0;
> -	while (nr_freed < tofree && !list_empty(&n->slabs_free)) {
> +	while (nr_freed < tofree && !list_empty_careful(&n->slabs_free)) {
>
>  		spin_lock_irq(&n->list_lock);
> -		p = n->slabs_free.prev;
> -		if (p == &n->slabs_free) {
> -			spin_unlock_irq(&n->list_lock);
> -			goto out;
> -		}
> -
> -		page = list_entry(p, struct page, lru);
> +		page = list_last_entry(&n->slabs_free, struct page, lru);

This is safe? Process could be rescheduled and lots of things could happen
before disabling irqs.
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