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

Nikolay Aleksandrov
2024-05-15T09:53:03Z

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@google.com>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz@google.com>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
>
> ---
>
> v7:
> - Updated SO_DEVMEM_* uapi to use the next available entry (Arnd).
>
> v6:
> - Squash in locking optimizations from edumazet@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);