Re: [PATCH v2 02/15] slab: add struct kmem_cache_args

[Mike Rapoport <rppt@kernel.org>]

On Wed, Sep 04, 2024 at 05:49:15PM +0200, Vlastimil Babka wrote:
> On 9/4/24 17:16, Mike Rapoport wrote:
> > On Tue, Sep 03, 2024 at 04:20:43PM +0200, Christian Brauner wrote:
> >> @@ -275,7 +285,7 @@ do_kmem_cache_create_usercopy(const char *name,
> >>  
> >>  	mutex_lock(&slab_mutex);
> >>  
> >> -	err = kmem_cache_sanity_check(name, size);
> >> +	err = kmem_cache_sanity_check(name, object_size);
> >>  	if (err) {
> >>  		goto out_unlock;
> >>  	}
> >> @@ -296,12 +306,14 @@ do_kmem_cache_create_usercopy(const char *name,
> >>  
> >>  	/* Fail closed on bad usersize of useroffset values. */
> >>  	if (!IS_ENABLED(CONFIG_HARDENED_USERCOPY) ||
> >> -	    WARN_ON(!usersize && useroffset) ||
> >> -	    WARN_ON(size < usersize || size - usersize < useroffset))
> >> -		usersize = useroffset = 0;
> >> -
> >> -	if (!usersize)
> >> -		s = __kmem_cache_alias(name, size, align, flags, ctor);
> >> +	    WARN_ON(!args->usersize && args->useroffset) ||
> >> +	    WARN_ON(object_size < args->usersize ||
> >> +		    object_size - args->usersize < args->useroffset))
> >> +		args->usersize = args->useroffset = 0;
> >> +
> >> +	if (!args->usersize)
> >> +		s = __kmem_cache_alias(name, object_size, args->align, flags,
> >> +				       args->ctor);
> > 
> > Sorry I missed it in the previous review, but nothing guaranties that
> > nobody will call kmem_cache_create_args with args != NULL.
> > 
> > I think there should be a check for args != NULL and a substitution of args
> > with defaults if it actually was NULL.
> 
> Hm there might be a bigger problem with this? If we wanted to do a
> (non-flag-day) conversion to the new kmem_cache_create() for some callers
> that need none of the extra args, passing NULL wouldn't work for the
> _Generic((__args) looking for "struct kmem_cache_args *" as NULL is not of
> that type, right?
> 
> I tried and it really errors out.

How about

#define kmem_cache_create(__name, __object_size, __args, ...)           \
	_Generic((__args),                                              \
		struct kmem_cache_args *: __kmem_cache_create_args,	\
		void *: __kmem_cache_create_args,			\
		default: __kmem_cache_create)(__name, __object_size, __args, __VA_ARGS__)

 

-- 
Sincerely yours,
Mike.