linux-kernel - Re: [PATCH] slab: add a check for the first kmem

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Message-ID: <alpine.DEB.2.10.1701171452580.142998@chino.kir.corp.google.com>
Date:   Tue, 17 Jan 2017 14:54:42 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     kwon <kwon@...nyone.net>
cc:     Joonsoo Kim <iamjoonsoo.kim@....com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] slab: add a check for the first kmem_cache not to be
 destroyed

On Tue, 17 Jan 2017, kwon wrote:

> >> diff --git a/mm/slab_common.c b/mm/slab_common.c
> >> index 1dfc209..2d30ace 100644
> >> --- a/mm/slab_common.c
> >> +++ b/mm/slab_common.c
> >> @@ -744,7 +744,7 @@ void kmem_cache_destroy(struct kmem_cache *s)
> >> 	bool need_rcu_barrier = false;
> >> 	int err;
> >> 
> >> -	if (unlikely(!s))
> >> +	if (unlikely(!s) || s->refcount == -1)
> >> 		return;
> > 
> > Hello, Kyunghwan.
> > 
> > Few lines below, s->refcount is checked.
> > 
> > if (s->refcount)
> >        goto unlock;
> > 
> > Am I missing something?
> > 
> > Thanks.
> 
> Hello, Joonsoo.
> 
> In case it is called the number of int size times. refcount would finally reach
> to 0 since decreased every time the function called.
> 

The only thing using create_boot_cache() should be the slab implementation 
itself, so I don't think we need to protect ourselves from doing something 
like kmem_cache_destroy(kmem_cache) or 
kmem_cache_destroy(kmem_cache_node) even a single time.