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

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Date:	Thu, 19 Dec 2013 13:26:12 +0400
From:	Vasily Averin <vvs@...allels.com>
To:	Vladimir Davydov <vdavydov@...allels.com>
CC:	Michal Hocko <mhocko@...e.cz>, 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 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.

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