Re: [Devel] [PATCH 1/6] slab: cleanup kmem_cache_create_memcg()

[Pekka Enberg]

On 12/19/2013 11:26 AM, 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.

I don't know what semantics you are referring to but a typical 
convention in mm/*.c is to return zero on success and negative on error 
but never positive numbers.

Looking at mm/slab_common.c, "if (err)" is the established convention so 
using "if (err < 0)" just because is pointless here.

                            Pekka
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