linux-kernel - Re: Duplicate kernel-doc comments for ksize()

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Date:   Mon, 7 Nov 2022 17:23:40 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Akira Yokosawa <akiyks@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>
Cc:     Jonathan Corbet <corbet@....net>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: Duplicate kernel-doc comments for ksize()

On 11/7/22 11:41, Akira Yokosawa wrote:
> Hi Kees,
> 
> "make htmldocs" reports duplicate C declaration of ksize()
> as follows:
> 
> /linux/Documentation/core-api/mm-api:43: ./mm/slab_common.c:1428: WARNING: Duplicate C declaration, also defined at core-api/mm-api:212.
> Declaration is '.. c:function:: size_t ksize (const void *objp)'.
> 
> This is due to the kernel-doc comment for ksize() added in
> include/linux/slab.h by a commit you have authored:
>   05a940656e1e ("slab:Introduce kmalloc_size_roundup()").
> 
> /**
>  * ksize - Report actual allocation size of associated object
>  *
>  * @objp: Pointer returned from a prior kmalloc()-family allocation.
>  *
>  * This should not be used for writing beyond the originally requested
>  * allocation size. Either use krealloc() or round up the allocation size
>  * with kmalloc_size_roundup() prior to allocation. If this is used to
>  * access beyond the originally requested allocation size, UBSAN_BOUNDS
>  * and/or FORTIFY_SOURCE may trip, since they only know about the
>  * originally allocated size via the __alloc_size attribute.
>  */
> 
> There is another kernel-doc comment in mm/slab_common.c (originally
> by Manfred, since v2.6.14):
> 
> /**
>  * ksize - get the actual amount of memory allocated for a given object
>  * @objp: Pointer to the object
>  *
>  * kmalloc may internally round up allocations and return more memory
>  * than requested. ksize() can be used to determine the actual amount of
>  * memory allocated. The caller may use this additional memory, even though
>  * a smaller amount of memory was initially specified with the kmalloc call.
>  * The caller must guarantee that objp points to a valid object previously
>  * allocated with either kmalloc() or kmem_cache_alloc(). The object
>  * must not be freed during the duration of the call.
>  *
>  * Return: size of the actual memory used by @objp in bytes
>  */
> 
> I guess the one in slab_common.c is outdated and can be removed.
> Can you please take care of it?

Thanks for the report, I've removed the comment myself in a slab.git fixes
branch I'll be sending a PR for this week:

https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git/commit/?h=slab/for-6.1-rc4/fixes&id=c18c20f16219516b12a4f2fd29c25e06be97e064

>         Thanks, Akira