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net: adding memory barrier to the poll and receive callbacks

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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>
This commit is contained in:
Jiri Olsa 2009-07-08 12:09:13 +00:00 committed by David S. Miller
parent 1b614fb9a0
commit a57de0b433
10 changed files with 85 additions and 19 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

66
include/net/sock.h
View file

@ -54,6 +54,7 @@
#include <linux/filter.h>
#include <linux/rculist_nulls.h>
#include <linux/poll.h>
#include <asm/atomic.h>
#include <net/dst.h>
@ -1241,6 +1242,71 @@ static inline int sk_has_allocations(const struct sock *sk)
return sk_wmem_alloc_get(sk) || sk_rmem_alloc_get(sk);
}
/**
* sk_has_sleeper - check if there are any waiting processes
* @sk: socket
*
* Returns true if socket has waiting processes
*
* The purpose of the sk_has_sleeper and sock_poll_wait is to wrap the memory
* barrier call. They were added due to the race found within the tcp code.
*
* Consider following tcp code paths:
*
* 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)
* ...
* }
*
* The race for tcp fires 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
* could then endup calling schedule and sleep forever if there are no more
* data on the socket.
*/
static inline int sk_has_sleeper(struct sock *sk)
{
/*
* We need to be sure we are in sync with the
* add_wait_queue modifications to the wait queue.
*
* This memory barrier is paired in the sock_poll_wait.
*/
smp_mb();
return sk->sk_sleep && waitqueue_active(sk->sk_sleep);
}
/**
* sock_poll_wait - place memory barrier behind the poll_wait call.
* @filp: file
* @wait_address: socket wait queue
* @p: poll_table
*
* See the comments in the sk_has_sleeper function.
*/
static inline void sock_poll_wait(struct file *filp,
wait_queue_head_t *wait_address, poll_table *p)
{
if (p && wait_address) {
poll_wait(filp, wait_address, p);
/*
* We need to be sure we are in sync with the
* socket flags modification.
*
* This memory barrier is paired in the sk_has_sleeper.
*/
smp_mb();
}
}
/*
* Queue a received datagram if it will fit. Stream and sequenced
* protocols can't normally use this as they need to fit buffers in

6
net/atm/common.c
View file

@ -92,7 +92,7 @@ static void vcc_sock_destruct(struct sock *sk)
static void vcc_def_wakeup(struct sock *sk)
{
read_lock(&sk->sk_callback_lock);
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up(sk->sk_sleep);
read_unlock(&sk->sk_callback_lock);
}
@ -110,7 +110,7 @@ static void vcc_write_space(struct sock *sk)
read_lock(&sk->sk_callback_lock);
if (vcc_writable(sk)) {
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible(sk->sk_sleep);
sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
@ -594,7 +594,7 @@ unsigned int vcc_poll(struct file *file, struct socket *sock, poll_table *wait)
struct atm_vcc *vcc;
unsigned int mask;
poll_wait(file, sk->sk_sleep, wait);
sock_poll_wait(file, sk->sk_sleep, wait);
mask = 0;
vcc = ATM_SD(sock);

2
net/core/datagram.c
View file

@ -712,7 +712,7 @@ unsigned int datagram_poll(struct file *file, struct socket *sock,
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? */

8
net/core/sock.c
View file

@ -1715,7 +1715,7 @@ EXPORT_SYMBOL(sock_no_sendpage);
static void sock_def_wakeup(struct sock *sk)
{
read_lock(&sk->sk_callback_lock);
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible_all(sk->sk_sleep);
read_unlock(&sk->sk_callback_lock);
}
@ -1723,7 +1723,7 @@ static void sock_def_wakeup(struct sock *sk)
static void sock_def_error_report(struct sock *sk)
{
read_lock(&sk->sk_callback_lock);
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible_poll(sk->sk_sleep, POLLERR);
sk_wake_async(sk, SOCK_WAKE_IO, POLL_ERR);
read_unlock(&sk->sk_callback_lock);
@ -1732,7 +1732,7 @@ static void sock_def_error_report(struct sock *sk)
static void sock_def_readable(struct sock *sk, int len)
{
read_lock(&sk->sk_callback_lock);
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible_sync_poll(sk->sk_sleep, POLLIN |
POLLRDNORM | POLLRDBAND);
sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
@ -1747,7 +1747,7 @@ static void sock_def_write_space(struct sock *sk)
* progress. --DaveM
*/
if ((atomic_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf) {
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible_sync_poll(sk->sk_sleep, POLLOUT |
POLLWRNORM | POLLWRBAND);

2
net/dccp/output.c
View file

@ -196,7 +196,7 @@ void dccp_write_space(struct sock *sk)
{
read_lock(&sk->sk_callback_lock);
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible(sk->sk_sleep);
/* Should agree with poll, otherwise some programs break */
if (sock_writeable(sk))

2
net/dccp/proto.c
View file

@ -311,7 +311,7 @@ unsigned int dccp_poll(struct file *file, struct socket *sock,
unsigned int mask;
struct sock *sk = sock->sk;
poll_wait(file, sk->sk_sleep, wait);
sock_poll_wait(file, sk->sk_sleep, wait);
if (sk->sk_state == DCCP_LISTEN)
return inet_csk_listen_poll(sk);

2
net/ipv4/tcp.c
View file

@ -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);

4
net/iucv/af_iucv.c
View file

@ -306,7 +306,7 @@ static inline int iucv_below_msglim(struct sock *sk)
static void iucv_sock_wake_msglim(struct sock *sk)
{
read_lock(&sk->sk_callback_lock);
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible_all(sk->sk_sleep);
sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
read_unlock(&sk->sk_callback_lock);
@ -1256,7 +1256,7 @@ unsigned int iucv_sock_poll(struct file *file, struct socket *sock,
struct sock *sk = sock->sk;
unsigned int mask = 0;
poll_wait(file, sk->sk_sleep, wait);
sock_poll_wait(file, sk->sk_sleep, wait);
if (sk->sk_state == IUCV_LISTEN)
return iucv_accept_poll(sk);

4
net/rxrpc/af_rxrpc.c
View file

@ -63,7 +63,7 @@ static void rxrpc_write_space(struct sock *sk)
_enter("%p", sk);
read_lock(&sk->sk_callback_lock);
if (rxrpc_writable(sk)) {
if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
if (sk_has_sleeper(sk))
wake_up_interruptible(sk->sk_sleep);
sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
}
@ -588,7 +588,7 @@ static unsigned int rxrpc_poll(struct file *file, struct socket *sock,
unsigned int mask;
struct sock *sk = sock->sk;
poll_wait(file, sk->sk_sleep, wait);
sock_poll_wait(file, sk->sk_sleep, wait);
mask = 0;
/* the socket is readable if there are any messages waiting on the Rx

8
net/unix/af_unix.c
View file

@ -315,7 +315,7 @@ static void unix_write_space(struct sock *sk)
{
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 @@ static unsigned int unix_poll(struct file *file, struct socket *sock, poll_table
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 @@ static unsigned int unix_dgram_poll(struct file *file, struct socket *sock,
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 @@ static unsigned int unix_dgram_poll(struct file *file, struct socket *sock,
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;