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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 3ff8bff704
"unix: Fix race in SOCK_SEQPACKET's unix_dgram_sendmsg()").

Thus, we do not need to take lock here.

Signed-off-by: Kirill Tkhai <tkhai@ya.ru>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Kirill Tkhai 2023-01-14 12:35:02 +03:00 committed by David S. Miller
parent 40ea3ee2ce
commit b27401a30e
1 changed files with 10 additions and 10 deletions
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20
net/unix/af_unix.c
View File

@ -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) static void unix_show_fdinfo(struct seq_file *m, struct socket *sock)
{ {
struct sock *sk = sock->sk; struct sock *sk = sock->sk;
unsigned char s_state;
struct unix_sock *u; struct unix_sock *u;
int nr_fds; int nr_fds = 0;
if (sk) { if (sk) {
s_state = READ_ONCE(sk->sk_state);
u = unix_sk(sk); 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); /* SOCK_STREAM and SOCK_SEQPACKET sockets never change their
if (sk->sk_state != TCP_LISTEN) * 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); nr_fds = atomic_read(&u->scm_stat.nr_fds);
else else if (s_state == TCP_LISTEN)
nr_fds = unix_count_nr_fds(sk); nr_fds = unix_count_nr_fds(sk);
unix_state_unlock(sk);
out_print:
seq_printf(m, "scm_fds: %u\n", nr_fds); seq_printf(m, "scm_fds: %u\n", nr_fds);
} }
} }