[PATCH] net: fix lock_sock_bh/unlock_sock_bh

Eric Dumazet
2010-05-27T05:06:08Z

Le mercredi 26 mai 2010 à 21:21 -0700, David Miller a écrit :
> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Thu, 27 May 2010 06:18:46 +0200
>
> > Process context :
> >
> > lock only (sk_lock.slock = locked, sk_lock.owned = ???)
> >
> > So I should add a test on owned. If set (by another thread), we should take the slow path.
>
> Indeed, what you're doing now is broken.
>
> If owned is non-zero when you take the spinlock you have to queue your
> work, just like how we toss packets into the socket backlog, which is
> processed by release_sock(), when this happens.

Here is the patch I am going to test today.

Anton, could you please test it too, just for sure ?

Thanks !

[PATCH] net: fix lock_sock_bh/unlock_sock_bh

This new sock lock primitive was introduced to speedup some user context
socket manipulation. But it is unsafe to protect two threads, one using
regular lock_sock/release_sock, one using lock_sock_bh/unlock_sock_bh

This patch changes lock_sock_bh to be careful against 'owned' state.
If owned is found to be set, we must take the slow path.
lock_sock_bh() now returns a boolean to say if the slow path was taken,
and this boolean is used at unlock_sock_bh time to call the appropriate
unlock function.

After this change, BH are either disabled or enabled during the
lock_sock_bh/unlock_sock_bh protected section. This might be misleading,
so we rename these functions to lock_sock_fast()/unlock_sock_fast().

Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
include/net/sock.h | 20 ++++++++++++++------
net/core/datagram.c | 6 ++++--
net/core/sock.c | 32 ++++++++++++++++++++++++++++++++
net/ipv4/udp.c | 14 ++++++++------
net/ipv6/udp.c | 5 +++--
5 files changed, 61 insertions(+), 16 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index d2a71b0..ca241ea 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1026,15 +1026,23 @@ extern void release_sock(struct sock *sk);
SINGLE_DEPTH_NESTING)
#define bh_unlock_sock(__sk) spin_unlock(&((__sk)->sk_lock.slock))

-static inline void lock_sock_bh(struct sock *sk)
+extern bool lock_sock_fast(struct sock *sk);
+/**
+ * unlock_sock_fast - complement of lock_sock_fast
+ * @sk: socket
+ * @slow: slow mode
+ *
+ * fast unlock socket for user context.
+ * If slow mode is on, we call regular release_sock()
+ */
+static inline void unlock_sock_fast(struct sock *sk, bool slow)
{
- spin_lock_bh(&sk->sk_lock.slock);
+ if (slow)
+ release_sock(sk);
+ else
+ spin_unlock_bh(&sk->sk_lock.slock);
}

-static inline void unlock_sock_bh(struct sock *sk)
-{
- spin_unlock_bh(&sk->sk_lock.slock);
-}

extern struct sock *sk_alloc(struct net *net, int family,
gfp_t priority,
diff --git a/net/core/datagram.c b/net/core/datagram.c
index e009753..f5b6f43 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -229,15 +229,17 @@ EXPORT_SYMBOL(skb_free_datagram);

void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
{
+ bool slow;
+
if (likely(atomic_read(&skb->users) == 1))
smp_rmb();
else if (likely(!atomic_dec_and_test(&skb->users)))
return;

- lock_sock_bh(sk);
+ slow = lock_sock_fast(sk);
skb_orphan(skb);
sk_mem_reclaim_partial(sk);
- unlock_sock_bh(sk);
+ unlock_sock_fast(sk, slow);

/* skb is now orphaned, can be freed outside of locked section */
__kfree_skb(skb);
diff --git a/net/core/sock.c b/net/core/sock.c
index 37fe9b6..7ab6398 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2007,6 +2007,38 @@ void release_sock(struct sock *sk)
}
EXPORT_SYMBOL(release_sock);

+/**
+ * lock_sock_fast - fast version of lock_sock
+ * @sk: socket
+ *
+ * This version should be used for very small section, where process wont block
+ * return false if fast path is taken
+ * sk_lock.slock locked, owned = 0, BH disabled
+ * return true if slow path is taken
+ * sk_lock.slock unlocked, owned = 1, BH enabled
+ */
+bool lock_sock_fast(struct sock *sk)
+{
+ might_sleep();
+ spin_lock_bh(&sk->sk_lock.slock);
+
+ if (!sk->sk_lock.owned)
+ /*
+ * Note : We must disable BH or risk a deadlock
+ */
+ return false;
+
+ __lock_sock(sk);
+ sk->sk_lock.owned = 1;
+ spin_unlock(&sk->sk_lock.slock);
+ /*
+ * The sk_lock has mutex_lock() semantics here:
+ */
+ mutex_acquire(&sk->sk_lock.dep_map, 0, 0, _RET_IP_);
+ return true;
+}
+EXPORT_SYMBOL(lock_sock_fast);
+
int sock_get_timestamp(struct sock *sk, struct timeval __user *userstamp)
{
struct timeval tv;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 9de6a69..b9d0d40 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1063,10 +1063,11 @@ static unsigned int first_packet_length(struct sock *sk)
spin_unlock_bh(&rcvq->lock);

if (!skb_queue_empty(&list_kill)) {
- lock_sock_bh(sk);
+ bool slow = lock_sock_fast(sk);
+
__skb_queue_purge(&list_kill);
sk_mem_reclaim_partial(sk);
- unlock_sock_bh(sk);
+ unlock_sock_fast(sk, slow);
}
return res;
}
@@ -1123,6 +1124,7 @@ int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
int peeked;
int err;
int is_udplite = IS_UDPLITE(sk);
+ bool slow;

/*
* Check any passed addresses
@@ -1197,10 +1199,10 @@ out:
return err;

csum_copy_err:
- lock_sock_bh(sk);
+ slow = lock_sock_fast(sk);
if (!skb_kill_datagram(sk, skb, flags))
UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
- unlock_sock_bh(sk);
+ unlock_sock_fast(sk, slow);

if (noblock)
return -EAGAIN;
@@ -1625,9 +1627,9 @@ int udp_rcv(struct sk_buff *skb)

void udp_destroy_sock(struct sock *sk)
{
- lock_sock_bh(sk);
+ bool slow = lock_sock_fast(sk);
udp_flush_pending_frames(sk);
- unlock_sock_bh(sk);
+ unlock_sock_fast(sk, slow);
}

/*
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 3d7a2c0..87be586 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -328,6 +328,7 @@ int udpv6_recvmsg(struct kiocb *iocb, struct sock *sk,
int err;
int is_udplite = IS_UDPLITE(sk);
int is_udp4;
+ bool slow;

if (addr_len)
*addr_len=sizeof(struct sockaddr_in6);
@@ -424,7 +425,7 @@ out:
return err;

csum_copy_err:
- lock_sock_bh(sk);
+ slow = lock_sock_fast(sk);
if (!skb_kill_datagram(sk, skb, flags)) {
if (is_udp4)
UDP_INC_STATS_USER(sock_net(sk),
@@ -433,7 +434,7 @@ csum_copy_err:
UDP6_INC_STATS_USER(sock_net(sk),
UDP_MIB_INERRORS, is_udplite);
}
- unlock_sock_bh(sk);
+ unlock_sock_fast(sk, slow);

if (flags & MSG_DONTWAIT)
return -EAGAIN;