Re: [PATCH net-next 1/4] net: unix: print cgroup_id and peer_cgroup_id in fdinfo

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Date: Sun,  9 Mar 2025 14:28:12 +0100

Please add few sentences here, why this interface is needed,
why accessing peer sk's sk_cgrp_data is not racy (e.g. sk_cgrp_data
never changes after creation (I'm not sure this is the case though)),
etc.

In case this interface is racy for the use case, please drop the patch.


> Cc: linux-kernel@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Cc: cgroups@vger.kernel.org
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Willem de Bruijn <willemb@google.com>
> Cc: Leon Romanovsky <leon@kernel.org>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Kuniyuki Iwashima <kuniyu@amazon.com>
> Cc: Lennart Poettering <mzxreary@0pointer.de>
> Cc: Luca Boccassi <bluca@debian.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: "Michal Koutný" <mkoutny@suse.com>
> Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
> ---
>  net/unix/af_unix.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 7f8f3859cdb3..2b2c0036efc9 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -117,6 +117,7 @@
>  #include <linux/file.h>
>  #include <linux/btf_ids.h>
>  #include <linux/bpf-cgroup.h>
> +#include <linux/cgroup.h>
>  
>  static atomic_long_t unix_nr_socks;
>  static struct hlist_head bsd_socket_buckets[UNIX_HASH_SIZE / 2];
> @@ -861,6 +862,11 @@ static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)
>  	int nr_fds = 0;
>  
>  	if (sk) {
> +#ifdef CONFIG_SOCK_CGROUP_DATA
> +		struct sock *peer;
> +		u64 sk_cgroup_id = 0;

Please keep reverse xmas tree order for net patches.
https://docs.kernel.org/process/maintainer-netdev.html#local-variable-ordering-reverse-xmas-tree-rcs

Also, no need to initialise sk_cgroup_id, so it should be:

	struct sock *peer;
	u64 sk_cgroup_id;


> +#endif
> +
>  		s_state = READ_ONCE(sk->sk_state);
>  		u = unix_sk(sk);
>  
> @@ -874,6 +880,21 @@ static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)
>  			nr_fds = unix_count_nr_fds(sk);
>  
>  		seq_printf(m, "scm_fds: %u\n", nr_fds);
> +
> +#ifdef CONFIG_SOCK_CGROUP_DATA
> +		sk_cgroup_id = cgroup_id(sock_cgroup_ptr(&sk->sk_cgrp_data));
> +		seq_printf(m, "cgroup_id: %llu\n", sk_cgroup_id);
> +
> +		peer = unix_peer_get(sk);
> +		if (peer) {
> +			u64 peer_cgroup_id = 0;

Same here, no need to initialise peer_cgroup_id.


> +
> +			peer_cgroup_id = cgroup_id(sock_cgroup_ptr(&peer->sk_cgrp_data));
> +			sock_put(peer);
> +
> +			seq_printf(m, "peer_cgroup_id: %llu\n", peer_cgroup_id);
> +		}
> +#endif
>  	}
>  }
>  #else
> -- 
> 2.43.0

Thanks!