linux-kernel - Re: [PATCH] slab+slob: dup name string

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Message-ID: <alpine.DEB.2.00.1205212018230.13522@chino.kir.corp.google.com>
Date:	Mon, 21 May 2012 20:22:25 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Glauber Costa <glommer@...allels.com>
cc:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] slab+slob: dup name string

On Mon, 21 May 2012, Glauber Costa wrote:

> diff --git a/mm/slab.c b/mm/slab.c
> index e901a36..cabd217 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2118,6 +2118,7 @@ static void __kmem_cache_destroy(struct kmem_cache *cachep)
>  			kfree(l3);
>  		}
>  	}
> +	kfree(cachep->name);
>  	kmem_cache_free(&cache_cache, cachep);
>  }
>  
> @@ -2526,9 +2527,14 @@ kmem_cache_create (const char *name, size_t size, size_t align,
>  		BUG_ON(ZERO_OR_NULL_PTR(cachep->slabp_cache));
>  	}
>  	cachep->ctor = ctor;
> -	cachep->name = name;
>  
> -	if (setup_cpu_cache(cachep, gfp)) {
> +	/* Can't do strdup while kmalloc is not up */
> +	if (g_cpucache_up > EARLY)
> +		cachep->name = kstrdup(name, GFP_KERNEL);
> +	else
> +		cachep->name = name;
> +
> +	if (!cachep->name || setup_cpu_cache(cachep, gfp)) {
>  		__kmem_cache_destroy(cachep);
>  		cachep = NULL;
>  		goto oops;

This doesn't work if you kmem_cache_destroy() a cache that was created 
when g_cpucache_cpu <= EARLY, the kfree() will explode.  That never 
happens for any existing cache created in kmem_cache_init(), but this 
would introduce the first roadblock in doing so.  So you'll need some 
magic to determine whether the cache was allocated statically and suppress 
the kfree() in such a case.
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