linux-kernel - Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create

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Date:	Thu, 19 Dec 2013 10:45:27 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Vasily Averin <vvs@...allels.com>
Cc:	Vladimir Davydov <vdavydov@...allels.com>,
	Glauber Costa <glommer@...il.com>,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
	linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>,
	cgroups@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>, devel@...nvz.org
Subject: Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg()

On Thu 19-12-13 13:26:12, Vasily Averin wrote:
> On 12/19/2013 12:39 PM, Vladimir Davydov wrote:
> > On 12/19/2013 12:17 PM, Vasily Averin wrote:
> >> On 12/18/2013 05:16 PM, Vladimir Davydov wrote:
> >>> --- a/mm/slab_common.c
> >>> +++ b/mm/slab_common.c
> >>> @@ -176,8 +176,9 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
> >>>  	get_online_cpus();
> >>>  	mutex_lock(&slab_mutex);
> >>>  
> >>> -	if (!kmem_cache_sanity_check(memcg, name, size) == 0)
> >>> -		goto out_locked;
> >>> +	err = kmem_cache_sanity_check(memcg, name, size);
> >>> +	if (err)
> >>> +		goto out_unlock;
> >>>  
> >>>  	/*
> >>>  	 * Some allocators will constraint the set of valid flags to a subset
> >> Theoretically in future kmem_cache_sanity_check() can return positive value.
> >> Probably it's better to check (err < 0) in caller ?
> > 
> > Hmm, why? What information could positive retval carry here? We have
> > plenty of places throughout the code where we check for (err), not
> > (err<0), simply because it looks clearer, e.g. look at
> > __kmem_cache_create() calls. If it returns a positive value one day, we
> > will have to parse every place where it's called. Anyway, if someone
> > wants to change a function behavior, he must check every place where
> > this function is called and fix them accordingly.
> 
> I believe expected semantic of function -- return negative in case of error.
> So correct error cheek should be (err < 0).
> (err) check is semantically incorrect, and it can lead to troubles in future.

No, this function returns -ERRNO or 0 on success.

-- 
Michal Hocko
SUSE Labs
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