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

[Christian Brauner <brauner@kernel.org>]

On Wed, Sep 04, 2024 at 10:13:11AM GMT, Vlastimil Babka wrote:
> On 9/3/24 16:20, Christian Brauner wrote:
> 
> You could describe that it's to hold less common args and there's
> __kmem_cache_create_args() that takes it, and
> do_kmem_cache_create_usercopy() is converted to it? Otherwise LGTM.

Hm, I seem to have dropped the contents of the commit message when I
split it into multiple individual commits. I've now added:

"Currently we have multiple kmem_cache_create*() variants that take up to
seven separate parameters with one of the functions having to grow an
eigth parameter in the future to handle both usercopy and a custom
freelist pointer.

Add a struct kmem_cache_args structure and move less common parameters
into it. Core parameters such as name, object size, and flags continue
to be passed separately.

Add a new function __kmem_cache_create_args() that takes a struct
kmem_cache_args pointer and port do_kmem_cache_create_usercopy() over to
it.

In follow-up patches we will port the other kmem_cache_create*()
variants over to it as well."

to the work.kmem_cache_args branch.

> 
> > Signed-off-by: Christian Brauner <brauner@kernel.org>
> > ---
> >  include/linux/slab.h | 21 ++++++++++++++++
> >  mm/slab_common.c     | 67 +++++++++++++++++++++++++++++++++++++++-------------
> >  2 files changed, 72 insertions(+), 16 deletions(-)
> > 
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 5b2da2cf31a8..79d8c8bca4a4 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -240,6 +240,27 @@ struct mem_cgroup;
> >   */
> >  bool slab_is_available(void);
> >  
> > +/**
> > + * @align: The required alignment for the objects.
> > + * @useroffset: Usercopy region offset
> > + * @usersize: Usercopy region size
> > + * @freeptr_offset: Custom offset for the free pointer in RCU caches
> > + * @use_freeptr_offset: Whether a @freeptr_offset is used
> > + * @ctor: A constructor for the objects.
> > + */
> > +struct kmem_cache_args {
> > +	unsigned int align;
> > +	unsigned int useroffset;
> > +	unsigned int usersize;
> > +	unsigned int freeptr_offset;
> > +	bool use_freeptr_offset;
> > +	void (*ctor)(void *);
> > +};
> > +
> > +struct kmem_cache *__kmem_cache_create_args(const char *name,
> > +					    unsigned int object_size,
> > +					    struct kmem_cache_args *args,
> > +					    slab_flags_t flags);
> >  struct kmem_cache *kmem_cache_create(const char *name, unsigned int size,
> >  			unsigned int align, slab_flags_t flags,
> >  			void (*ctor)(void *));
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index 91e0e36e4379..0f13c045b8d1 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -248,14 +248,24 @@ static struct kmem_cache *create_cache(const char *name,
> >  	return ERR_PTR(err);
> >  }
> >  
> > -static struct kmem_cache *
> > -do_kmem_cache_create_usercopy(const char *name,
> > -		  unsigned int size, unsigned int freeptr_offset,
> > -		  unsigned int align, slab_flags_t flags,
> > -		  unsigned int useroffset, unsigned int usersize,
> > -		  void (*ctor)(void *))
> > +/**
> > + * __kmem_cache_create_args - Create a kmem cache
> > + * @name: A string which is used in /proc/slabinfo to identify this cache.
> > + * @object_size: The size of objects to be created in this cache.
> > + * @args: Arguments for the cache creation (see struct kmem_cache_args).
> > + * @flags: See %SLAB_* flags for an explanation of individual @flags.
> > + *
> > + * Cannot be called within a interrupt, but can be interrupted.
> > + *
> > + * Return: a pointer to the cache on success, NULL on failure.
> > + */
> > +struct kmem_cache *__kmem_cache_create_args(const char *name,
> > +					    unsigned int object_size,
> > +					    struct kmem_cache_args *args,
> > +					    slab_flags_t flags)
> >  {
> >  	struct kmem_cache *s = NULL;
> > +	unsigned int freeptr_offset = UINT_MAX;
> >  	const char *cache_name;
> >  	int err;
> >  
> > @@ -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);
> >  	if (s)
> >  		goto out_unlock;
> >  
> > @@ -311,9 +323,11 @@ do_kmem_cache_create_usercopy(const char *name,
> >  		goto out_unlock;
> >  	}
> >  
> > -	s = create_cache(cache_name, size, freeptr_offset,
> > -			 calculate_alignment(flags, align, size),
> > -			 flags, useroffset, usersize, ctor);
> > +	if (args->use_freeptr_offset)
> > +		freeptr_offset = args->freeptr_offset;
> > +	s = create_cache(cache_name, object_size, freeptr_offset,
> > +			 calculate_alignment(flags, args->align, object_size),
> > +			 flags, args->useroffset, args->usersize, args->ctor);
> >  	if (IS_ERR(s)) {
> >  		err = PTR_ERR(s);
> >  		kfree_const(cache_name);
> > @@ -335,6 +349,27 @@ do_kmem_cache_create_usercopy(const char *name,
> >  	}
> >  	return s;
> >  }
> > +EXPORT_SYMBOL(__kmem_cache_create_args);
> > +
> > +static struct kmem_cache *
> > +do_kmem_cache_create_usercopy(const char *name,
> > +                 unsigned int size, unsigned int freeptr_offset,
> > +                 unsigned int align, slab_flags_t flags,
> > +                 unsigned int useroffset, unsigned int usersize,
> > +                 void (*ctor)(void *))
> > +{
> > +	struct kmem_cache_args kmem_args = {
> > +		.align			= align,
> > +		.use_freeptr_offset	= freeptr_offset != UINT_MAX,
> > +		.freeptr_offset		= freeptr_offset,
> > +		.useroffset		= useroffset,
> > +		.usersize		= usersize,
> > +		.ctor			= ctor,
> > +	};
> > +
> > +	return __kmem_cache_create_args(name, size, &kmem_args, flags);
> > +}
> > +
> >  
> >  /**
> >   * kmem_cache_create_usercopy - Create a cache with a region suitable
> > 
>