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 <jolsa@redhat.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 36d4e44..fc3ebb9 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -315,7 +315,7 @@
{
read_lock(&sk->sk_callback_lock);
if (unix_writable(sk)) {
- if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
+ if (sk_has_sleeper(sk))
wake_up_interruptible_sync(sk->sk_sleep);
sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
}
@@ -1985,7 +1985,7 @@
struct sock *sk = sock->sk;
unsigned int mask;
- poll_wait(file, sk->sk_sleep, wait);
+ sock_poll_wait(file, sk->sk_sleep, wait);
mask = 0;
/* exceptional events? */
@@ -2022,7 +2022,7 @@
struct sock *sk = sock->sk, *other;
unsigned int mask, writable;
- poll_wait(file, sk->sk_sleep, wait);
+ sock_poll_wait(file, sk->sk_sleep, wait);
mask = 0;
/* exceptional events? */
@@ -2053,7 +2053,7 @@
other = unix_peer_get(sk);
if (other) {
if (unix_peer(other) != sk) {
- poll_wait(file, &unix_sk(other)->peer_wait,
+ sock_poll_wait(file, &unix_sk(other)->peer_wait,
wait);
if (unix_recvq_full(other))
writable = 0;