Re: [PATCH] net: fix lock_sock_bh/unlock_sock_bh

Eric Dumazet
2010-05-27T05:20:27Z

Le jeudi 27 mai 2010 à 07:06 +0200, Eric Dumazet a écrit :
> 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_);

Oops, I missed a local_bh_enable(); here

> + return true;
> +}
> +EXPORT_SYMBOL(lock_sock_fast);
> +
> int sock_get_timestamp(struct sock *sk, struct timeval __user *userstamp)
> {
> struct timeval tv;

Here is v2 of patch with local_bh_enable(); added in lock_sock_fast()

[PATCH v2] 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 | 33 +++++++++++++++++++++++++++++++++
net/ipv4/udp.c | 14 ++++++++------
net/ipv6/udp.c | 5 +++--
5 files changed, 62 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..2cf7f9f 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2007,6 +2007,39 @@ 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
+ */
+ 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_);
+ local_bh_enable();
+ 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;