Subject: Re: [PATCH net-next 01/17] net: Copy slab data for sendmsg(MSG_SPLICE_PAGES)

From: Simon Horman <[email-masked]>
Date: Fri, 16 Jun 2023 21:49:45 +0200

On Fri, Jun 16, 2023 at 05:12:44PM +0100, David Howells wrote:

...

> +/**
> + * alloc_skb_frag - Allocate a page fragment for using in a socket
> + * @fragsz: The size of fragment required
> + * @gfp: Allocation flags
> + */
> +void *alloc_skb_frag(size_t fragsz, gfp_t gfp)
> +{
> +	struct skb_splice_frag_cache *cache;
> +	struct folio *folio, *spare = NULL;
> +	size_t offset, fsize;
> +	void *p;
> +
> +	if (WARN_ON_ONCE(fragsz == 0))
> +		fragsz = 1;
> +
> +	cache = get_cpu_ptr(&skb_splice_frag_cache);
> +reload:
> +	folio = cache->folio;
> +	offset = cache->offset;
> +try_again:
> +	if (fragsz > offset)
> +		goto insufficient_space;
> +
> +	/* Make the allocation. */
> +	cache->pagecnt_bias--;
> +	offset = ALIGN_DOWN(offset - fragsz, SMP_CACHE_BYTES);
> +	cache->offset = offset;
> +	p = cache->virt + offset;
> +	put_cpu_ptr(skb_splice_frag_cache);

Hi David,

I don't think it makes any difference at run-time.
But to keep Sparse happy, perhaps this ought to be put_cpu_var()

...