netdev - Re: [PATCH 1/2][net-next] skbuff: move netlink_large_alloc_large

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Message-ID: <50622ac2-0939-af35-5d62-c56249e7bd26@huawei.com>
Date: Thu, 2 Nov 2023 19:01:53 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Li RongQing <lirongqing@...du.com>, <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/2][net-next] skbuff: move
 netlink_large_alloc_large_skb() to skbuff.c

On 2023/11/2 14:28, Li RongQing wrote:
> move netlink_alloc_large_skb and netlink_skb_destructor to skbuff.c
> and rename them more generic, so they can be used elsewhere large
> non-contiguous physical memory is needed
> 
> Signed-off-by: Li RongQing <lirongqing@...du.com>
> ---
>  include/linux/skbuff.h   |  3 +++
>  net/core/skbuff.c        | 40 ++++++++++++++++++++++++++++++++++++++++
>  net/netlink/af_netlink.c | 41 ++---------------------------------------
>  3 files changed, 45 insertions(+), 39 deletions(-)
> 
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 4174c4b..774a401 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -5063,5 +5063,8 @@ static inline void skb_mark_for_recycle(struct sk_buff *skb)
>  ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter,
>  			     ssize_t maxsize, gfp_t gfp);
>  
> +
> +void large_skb_destructor(struct sk_buff *skb);
> +struct sk_buff *alloc_large_skb(unsigned int size, int broadcast);
>  #endif	/* __KERNEL__ */
>  #endif	/* _LINUX_SKBUFF_H */
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 4570705..20ffcd5 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -6917,3 +6917,43 @@ ssize_t skb_splice_from_iter(struct sk_buff *skb, struct iov_iter *iter,
>  	return spliced ?: ret;
>  }
>  EXPORT_SYMBOL(skb_splice_from_iter);
> +
> +void large_skb_destructor(struct sk_buff *skb)
> +{
> +	if (is_vmalloc_addr(skb->head)) {
> +		if (!skb->cloned ||
> +		    !atomic_dec_return(&(skb_shinfo(skb)->dataref)))
> +			vfree(skb->head);
> +
> +		skb->head = NULL;

There seems to be an assumption that skb returned from
netlink_alloc_large_skb() is not expecting the frag page
for shinfo->frags*, as the above NULL setting will bypass
most of the handling in skb_release_data(),then how can we
ensure that the user is not breaking the assumption if we
make it more generic?


> +	}
> +	if (skb->sk)
> +		sock_rfree(skb);
> +}
> +EXPORT_SYMBOL(large_skb_destructor);
> +