Re: [PATCH] zsmalloc: fix a null pointer dereference in destroy_handle_cache()

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 9 Jun 2015 09:38:27 +0900 Joonsoo Kim <iamjoonsoo.kim@lge.com> wrote:

> > > ...
> > >
> > > --- a/mm/zsmalloc.c
> > > +++ b/mm/zsmalloc.c
> > > @@ -285,7 +285,8 @@ static int create_handle_cache(struct zs_pool *pool)
> > >  
> > >  static void destroy_handle_cache(struct zs_pool *pool)
> > >  {
> > > -	kmem_cache_destroy(pool->handle_cachep);
> > > +	if (pool->handle_cachep)
> > > +		kmem_cache_destroy(pool->handle_cachep);
> > >  }
> > >  
> > >  static unsigned long alloc_handle(struct zs_pool *pool)
> > 
> > I'll apply this, but...  from a bit of grepping I'm estimating that we
> > have approximately 200 instances of
> > 
> > 	if (foo)
> > 		kmem_cache_destroy(foo);
> > 
> > so obviously kmem_cache_destroy() should be doing the check.
> 
> Hello, Andrew.
> 
> I'm not sure if doing the check in kmem_cache_destroy() is better.

Of course it's better - we have *hundreds* of sites doing something
which could be done at a single site.  Where's the advantage in that?

> My quick grep for other pool based allocators(ex. mempool, zpool) also
> says that they don't check whether passed pool pointer is NULL or not
> in destroy function.

Maybe some of those should be converted as well.

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