From a57de0b4336e48db2811a2030bb68dba8dd09d88 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Wed, 8 Jul 2009 12:09:13 +0000 Subject: net: adding memory barrier to the poll and receive callbacks Adding memory barrier after the poll_wait function, paired with receive callbacks. Adding fuctions sock_poll_wait and sk_has_sleeper to wrap the memory barrier. Without the memory barrier, following race can happen. The race fires, when following code paths meet, and the tp->rcv_nxt and __add_wait_queue updates stay in CPU caches. CPU1 CPU2 sys_select receive packet ... ... __add_wait_queue update tp->rcv_nxt ... ... tp->rcv_nxt check sock_def_readable ... { schedule ... if (sk->sk_sleep && waitqueue_active(sk->sk_sleep)) wake_up_interruptible(sk->sk_sleep) ... } If there was no cache the code would work ok, since the wait_queue and rcv_nxt are opposit to each other. Meaning that once tp->rcv_nxt is updated by CPU2, the CPU1 either already passed the tp->rcv_nxt check and sleeps, or will get the new value for tp->rcv_nxt and will return with new data mask. In both cases the process (CPU1) is being added to the wait queue, so the waitqueue_active (CPU2) call cannot miss and will wake up CPU1. The bad case is when the __add_wait_queue changes done by CPU1 stay in its cache, and so does the tp->rcv_nxt update on CPU2 side. The CPU1 will then endup calling schedule and sleep forever if there are no more data on the socket. Calls to poll_wait in following modules were ommited: net/bluetooth/af_bluetooth.c net/irda/af_irda.c net/irda/irnet/irnet_ppp.c net/mac80211/rc80211_pid_debugfs.c net/phonet/socket.c net/rds/af_rds.c net/rfkill/core.c net/sunrpc/cache.c net/sunrpc/rpc_pipe.c net/tipc/socket.c Signed-off-by: Jiri Olsa Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/ipv4') diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 7870a535dac6..91145244ea63 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -339,7 +339,7 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait) struct sock *sk = sock->sk; struct tcp_sock *tp = tcp_sk(sk); - poll_wait(file, sk->sk_sleep, wait); + sock_poll_wait(file, sk->sk_sleep, wait); if (sk->sk_state == TCP_LISTEN) return inet_csk_listen_poll(sk); -- cgit v1.2.3