Commit b27401a3 authored by Kirill Tkhai's avatar Kirill Tkhai Committed by David S. Miller
Browse files

unix: Improve locking scheme in unix_show_fdinfo() 



After switching to TCP_ESTABLISHED or TCP_LISTEN sk_state, alive SOCK_STREAM
and SOCK_SEQPACKET sockets can't change it anymore (since commit 3ff8bff7
"unix: Fix race in SOCK_SEQPACKET's unix_dgram_sendmsg()").

Thus, we do not need to take lock here.

Signed-off-by: default avatarKirill Tkhai <tkhai@ya.ru>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 40ea3ee2

net/unix/af_unix.c

+10 −10
Original line number Diff line number Diff line
@@ -807,23 +807,23 @@ static int unix_count_nr_fds(struct sock *sk) 
static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)

{

	struct sock *sk = sock->sk;

	unsigned char s_state;

	struct unix_sock *u;

	int nr_fds;

	int nr_fds = 0;



	if (sk) {

		s_state = READ_ONCE(sk->sk_state);

		u = unix_sk(sk);

		if (sock->type == SOCK_DGRAM) {

			nr_fds = atomic_read(&u->scm_stat.nr_fds);

			goto out_print;

		}



		unix_state_lock(sk);

		if (sk->sk_state != TCP_LISTEN)

		/* SOCK_STREAM and SOCK_SEQPACKET sockets never change their

		 * sk_state after switching to TCP_ESTABLISHED or TCP_LISTEN.

		 * SOCK_DGRAM is ordinary. So, no lock is needed.

		 */

		if (sock->type == SOCK_DGRAM || s_state == TCP_ESTABLISHED)

			nr_fds = atomic_read(&u->scm_stat.nr_fds);

		else

		else if (s_state == TCP_LISTEN)

			nr_fds = unix_count_nr_fds(sk);

		unix_state_unlock(sk);

out_print:



		seq_printf(m, "scm_fds: %u\n", nr_fds);

	}

}