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tcp: ensure proper barriers in lockless contexts
Some functions access TCP sockets without holding a lock and might output non consistent data, depending on compiler and or architecture. tcp_diag_get_info(), tcp_get_info(), tcp_poll(), get_tcp4_sock() ... Introduce sk_state_load() and sk_state_store() to fix the issues, and more clearly document where this lack of locking is happening. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
David S. Miller
parent
5883d9c6d7
commit
00fd38d938
@ -2226,6 +2226,31 @@ static inline bool sk_listener(const struct sock *sk)
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return (1 << sk->sk_state) & (TCPF_LISTEN | TCPF_NEW_SYN_RECV);
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}
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/**
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* sk_state_load - read sk->sk_state for lockless contexts
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* @sk: socket pointer
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*
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* Paired with sk_state_store(). Used in places we do not hold socket lock :
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* tcp_diag_get_info(), tcp_get_info(), tcp_poll(), get_tcp4_sock() ...
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*/
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static inline int sk_state_load(const struct sock *sk)
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{
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return smp_load_acquire(&sk->sk_state);
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}
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/**
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* sk_state_store - update sk->sk_state
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* @sk: socket pointer
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* @newstate: new state
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*
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* Paired with sk_state_load(). Should be used in contexts where
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* state change might impact lockless readers.
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*/
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static inline void sk_state_store(struct sock *sk, int newstate)
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{
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smp_store_release(&sk->sk_state, newstate);
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}
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void sock_enable_timestamp(struct sock *sk, int flag);
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int sock_get_timestamp(struct sock *, struct timeval __user *);
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int sock_get_timestampns(struct sock *, struct timespec __user *);
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@ -563,7 +563,7 @@ static void reqsk_timer_handler(unsigned long data)
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int max_retries, thresh;
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u8 defer_accept;
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if (sk_listener->sk_state != TCP_LISTEN)
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if (sk_state_load(sk_listener) != TCP_LISTEN)
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goto drop;
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max_retries = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
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@ -749,7 +749,7 @@ int inet_csk_listen_start(struct sock *sk, int backlog)
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* It is OK, because this socket enters to hash table only
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* after validation is complete.
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*/
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sk->sk_state = TCP_LISTEN;
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sk_state_store(sk, TCP_LISTEN);
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if (!sk->sk_prot->get_port(sk, inet->inet_num)) {
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inet->inet_sport = htons(inet->inet_num);
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@ -451,11 +451,14 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
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unsigned int mask;
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struct sock *sk = sock->sk;
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const struct tcp_sock *tp = tcp_sk(sk);
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int state;
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sock_rps_record_flow(sk);
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sock_poll_wait(file, sk_sleep(sk), wait);
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if (sk->sk_state == TCP_LISTEN)
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state = sk_state_load(sk);
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if (state == TCP_LISTEN)
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return inet_csk_listen_poll(sk);
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/* Socket is not locked. We are protected from async events
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@ -492,14 +495,14 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
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* NOTE. Check for TCP_CLOSE is added. The goal is to prevent
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* blocking on fresh not-connected or disconnected socket. --ANK
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*/
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if (sk->sk_shutdown == SHUTDOWN_MASK || sk->sk_state == TCP_CLOSE)
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if (sk->sk_shutdown == SHUTDOWN_MASK || state == TCP_CLOSE)
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mask |= POLLHUP;
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if (sk->sk_shutdown & RCV_SHUTDOWN)
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mask |= POLLIN | POLLRDNORM | POLLRDHUP;
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/* Connected or passive Fast Open socket? */
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if (sk->sk_state != TCP_SYN_SENT &&
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(sk->sk_state != TCP_SYN_RECV || tp->fastopen_rsk)) {
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if (state != TCP_SYN_SENT &&
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(state != TCP_SYN_RECV || tp->fastopen_rsk)) {
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int target = sock_rcvlowat(sk, 0, INT_MAX);
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if (tp->urg_seq == tp->copied_seq &&
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@ -507,9 +510,6 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
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tp->urg_data)
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target++;
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/* Potential race condition. If read of tp below will
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* escape above sk->sk_state, we can be illegally awaken
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* in SYN_* states. */
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if (tp->rcv_nxt - tp->copied_seq >= target)
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mask |= POLLIN | POLLRDNORM;
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@ -1934,7 +1934,7 @@ void tcp_set_state(struct sock *sk, int state)
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/* Change state AFTER socket is unhashed to avoid closed
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* socket sitting in hash tables.
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*/
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sk->sk_state = state;
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sk_state_store(sk, state);
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#ifdef STATE_TRACE
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SOCK_DEBUG(sk, "TCP sk=%p, State %s -> %s\n", sk, statename[oldstate], statename[state]);
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@ -2644,7 +2644,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
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if (sk->sk_type != SOCK_STREAM)
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return;
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info->tcpi_state = sk->sk_state;
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info->tcpi_state = sk_state_load(sk);
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info->tcpi_ca_state = icsk->icsk_ca_state;
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info->tcpi_retransmits = icsk->icsk_retransmits;
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info->tcpi_probes = icsk->icsk_probes_out;
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@ -2672,7 +2673,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
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info->tcpi_snd_mss = tp->mss_cache;
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info->tcpi_rcv_mss = icsk->icsk_ack.rcv_mss;
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if (sk->sk_state == TCP_LISTEN) {
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if (info->tcpi_state == TCP_LISTEN) {
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info->tcpi_unacked = sk->sk_ack_backlog;
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info->tcpi_sacked = sk->sk_max_ack_backlog;
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} else {
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@ -21,7 +21,7 @@ static void tcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
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{
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struct tcp_info *info = _info;
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if (sk->sk_state == TCP_LISTEN) {
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if (sk_state_load(sk) == TCP_LISTEN) {
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r->idiag_rqueue = sk->sk_ack_backlog;
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r->idiag_wqueue = sk->sk_max_ack_backlog;
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} else if (sk->sk_type == SOCK_STREAM) {
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@ -2158,6 +2158,7 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
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__u16 destp = ntohs(inet->inet_dport);
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__u16 srcp = ntohs(inet->inet_sport);
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int rx_queue;
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int state;
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if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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@ -2175,17 +2176,18 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
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timer_expires = jiffies;
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}
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if (sk->sk_state == TCP_LISTEN)
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state = sk_state_load(sk);
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if (state == TCP_LISTEN)
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rx_queue = sk->sk_ack_backlog;
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else
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/*
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* because we dont lock socket, we might find a transient negative value
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/* Because we don't lock the socket,
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* we might find a transient negative value.
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*/
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rx_queue = max_t(int, tp->rcv_nxt - tp->copied_seq, 0);
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seq_printf(f, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX "
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"%08X %5u %8d %lu %d %pK %lu %lu %u %u %d",
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i, src, srcp, dest, destp, sk->sk_state,
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i, src, srcp, dest, destp, state,
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tp->write_seq - tp->snd_una,
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rx_queue,
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timer_active,
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@ -2199,8 +2201,8 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
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jiffies_to_clock_t(icsk->icsk_ack.ato),
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(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
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tp->snd_cwnd,
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sk->sk_state == TCP_LISTEN ?
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(fastopenq ? fastopenq->max_qlen : 0) :
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state == TCP_LISTEN ?
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fastopenq->max_qlen :
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(tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh));
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}
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@ -1690,6 +1690,8 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
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const struct tcp_sock *tp = tcp_sk(sp);
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const struct inet_connection_sock *icsk = inet_csk(sp);
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const struct fastopen_queue *fastopenq = &icsk->icsk_accept_queue.fastopenq;
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int rx_queue;
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int state;
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dest = &sp->sk_v6_daddr;
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src = &sp->sk_v6_rcv_saddr;
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@ -1710,6 +1712,15 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
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timer_expires = jiffies;
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}
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state = sk_state_load(sp);
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if (state == TCP_LISTEN)
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rx_queue = sp->sk_ack_backlog;
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else
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/* Because we don't lock the socket,
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* we might find a transient negative value.
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*/
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rx_queue = max_t(int, tp->rcv_nxt - tp->copied_seq, 0);
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seq_printf(seq,
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"%4d: %08X%08X%08X%08X:%04X %08X%08X%08X%08X:%04X "
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"%02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %lu %lu %u %u %d\n",
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@ -1718,9 +1729,9 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
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src->s6_addr32[2], src->s6_addr32[3], srcp,
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dest->s6_addr32[0], dest->s6_addr32[1],
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dest->s6_addr32[2], dest->s6_addr32[3], destp,
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sp->sk_state,
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tp->write_seq-tp->snd_una,
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(sp->sk_state == TCP_LISTEN) ? sp->sk_ack_backlog : (tp->rcv_nxt - tp->copied_seq),
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state,
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tp->write_seq - tp->snd_una,
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rx_queue,
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timer_active,
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jiffies_delta_to_clock_t(timer_expires - jiffies),
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icsk->icsk_retransmits,
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@ -1732,7 +1743,7 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
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jiffies_to_clock_t(icsk->icsk_ack.ato),
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(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
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tp->snd_cwnd,
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sp->sk_state == TCP_LISTEN ?
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state == TCP_LISTEN ?
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fastopenq->max_qlen :
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(tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh)
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);
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