[PATCH net-next v9 12/14] net: add SO_DEVMEM_DONTNEED setsockopt to release RX frags

[Nikolay Aleksandrov]

On 11/05/2024 02:21, Mina Almasry wrote:
> Add an interface for the user to notify the kernel that it is done
> reading the devmem dmabuf frags returned as cmsg. The kernel will
> drop the reference on the frags to make them available for reuse.
> 
> Signed-off-by: Willem de Bruijn <willemb at google.com>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz at google.com>
> Signed-off-by: Mina Almasry <almasrymina at google.com>
> 
> ---
> 
> v7:
> - Updated SO_DEVMEM_* uapi to use the next available entry (Arnd).
> 
> v6:
> - Squash in locking optimizations from edumazet at google.com. With his
>   changes we lock the xarray once per sock_devmem_dontneed operation
>   rather than once per frag.
> 
> Changes in v1:
> - devmemtoken -> dmabuf_token (David).
> - Use napi_pp_put_page() for refcounting (Yunsheng).
> - Fix build error with missing socket options on other asms.
> 
> ---
>  arch/alpha/include/uapi/asm/socket.h  |  1 +
>  arch/mips/include/uapi/asm/socket.h   |  1 +
>  arch/parisc/include/uapi/asm/socket.h |  1 +
>  arch/sparc/include/uapi/asm/socket.h  |  1 +
>  include/uapi/asm-generic/socket.h     |  1 +
>  include/uapi/linux/uio.h              |  4 ++
>  net/core/sock.c                       | 61 +++++++++++++++++++++++++++
>  7 files changed, 70 insertions(+)
> 
[snip]
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 8d6e638b5426d..2edb988259e8d 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -124,6 +124,7 @@
>  #include <linux/netdevice.h>
>  #include <net/protocol.h>
>  #include <linux/skbuff.h>
> +#include <linux/skbuff_ref.h>
>  #include <net/net_namespace.h>
>  #include <net/request_sock.h>
>  #include <net/sock.h>
> @@ -1049,6 +1050,62 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_PAGE_POOL
> +static noinline_for_stack int
> +sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
> +{
> +	unsigned int num_tokens, i, j, k, netmem_num = 0;
> +	struct dmabuf_token *tokens;
> +	netmem_ref netmems[16];
> +	int ret;
> +
> +	if (sk->sk_type != SOCK_STREAM || sk->sk_protocol != IPPROTO_TCP)
> +		return -EBADF;
> +
> +	if (optlen % sizeof(struct dmabuf_token) ||
> +	    optlen > sizeof(*tokens) * 128)
> +		return -EINVAL;
> +
> +	tokens = kvmalloc_array(128, sizeof(*tokens), GFP_KERNEL);
> +	if (!tokens)
> +		return -ENOMEM;
> +
> +	num_tokens = optlen / sizeof(struct dmabuf_token);
> +	if (copy_from_sockptr(tokens, optval, optlen))
> +		return -EFAULT;

tokens isn't freed in this error case

> +
> +	ret = 0;
> +
> +	xa_lock_bh(&sk->sk_user_frags);
> +	for (i = 0; i < num_tokens; i++) {
> +		for (j = 0; j < tokens[i].token_count; j++) {
> +			netmem_ref netmem = (__force netmem_ref)__xa_erase(
> +				&sk->sk_user_frags, tokens[i].token_start + j);
> +
> +			if (netmem &&
> +			    !WARN_ON_ONCE(!netmem_is_net_iov(netmem))) {
> +				netmems[netmem_num++] = netmem;
> +				if (netmem_num == ARRAY_SIZE(netmems)) {
> +					xa_unlock_bh(&sk->sk_user_frags);
> +					for (k = 0; k < netmem_num; k++)
> +						WARN_ON_ONCE(!napi_pp_put_page(netmems[k]));
> +					netmem_num = 0;
> +					xa_lock_bh(&sk->sk_user_frags);
> +				}
> +				ret++;
> +			}
> +		}
> +	}
> +
> +	xa_unlock_bh(&sk->sk_user_frags);
> +	for (k = 0; k < netmem_num; k++)
> +		WARN_ON_ONCE(!napi_pp_put_page(netmems[k]));
> +
> +	kvfree(tokens);
> +	return ret;
> +}
> +#endif
> +
>  void sockopt_lock_sock(struct sock *sk)
>  {
>  	/* When current->bpf_ctx is set, the setsockopt is called from
> @@ -1200,6 +1257,10 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
>  			ret = -EOPNOTSUPP;
>  		return ret;
>  		}
> +#ifdef CONFIG_PAGE_POOL
> +	case SO_DEVMEM_DONTNEED:
> +		return sock_devmem_dontneed(sk, optval, optlen);
> +#endif
>  	}
>  
>  	sockopt_lock_sock(sk);