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Subject[PATCH 1/2] 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 sock_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

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>

---
include/linux/poll.h | 11 +++++++++--
include/net/sock.h | 40 ++++++++++++++++++++++++++++++++++++++++
net/atm/common.c | 6 +++---
net/core/datagram.c | 2 +-
net/core/sock.c | 8 ++++----
net/dccp/output.c | 2 +-
net/dccp/proto.c | 2 +-
net/ipv4/tcp.c | 2 +-
net/iucv/af_iucv.c | 4 ++--
net/rxrpc/af_rxrpc.c | 4 ++--
net/unix/af_unix.c | 8 ++++----
11 files changed, 68 insertions(+), 21 deletions(-)

diff --git a/include/linux/poll.h b/include/linux/poll.h
index fa287f2..b2ea8ef 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -35,10 +35,17 @@ typedef struct poll_table_struct {
unsigned long key;
} poll_table;

-static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p)
+static inline void __poll_wait(struct file *filp,
+ wait_queue_head_t *wait_address, poll_table *p)
+{
+ p->qproc(filp, wait_address, p);
+}
+
+static inline void poll_wait(struct file *filp,
+ wait_queue_head_t *wait_address, poll_table *p)
{
if (p && wait_address)
- p->qproc(filp, wait_address, p);
+ __poll_wait(filp, wait_address, p);
}

static inline void init_poll_funcptr(poll_table *pt, poll_queue_proc qproc)
diff --git a/include/net/sock.h b/include/net/sock.h
index 352f06b..e9137ed 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -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 +1242,45 @@ 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
+ */
+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
+ * @sk: socket
+ * @p: poll_table
+ */
+static inline void sock_poll_wait(struct file *filp, struct sock *sk,
+ poll_table *p)
+{
+ if (p && sk->sk_sleep) {
+ __poll_wait(filp, sk->sk_sleep, 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
diff --git a/net/atm/common.c b/net/atm/common.c
index c1c9793..8c4d843 100644
--- a/net/atm/common.c
+++ b/net/atm/common.c
@@ -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);
diff --git a/net/core/datagram.c b/net/core/datagram.c
index 58abee1..b0fe692 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -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? */
diff --git a/net/core/sock.c b/net/core/sock.c
index b0ba569..6354863 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -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);

diff --git a/net/dccp/output.c b/net/dccp/output.c
index c0e88c1..c96119f 100644
--- a/net/dccp/output.c
+++ b/net/dccp/output.c
@@ -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))
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index 314a1b5..94ca8ea 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -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);

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 17b89c5..aa0ac36 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);

diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index 6be5f92..49c15b4 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -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);
diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index eac5e7b..bfe493e 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -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
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 @@ 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;

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