Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757056AbZGGP5R (ORCPT ); Tue, 7 Jul 2009 11:57:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754959AbZGGP47 (ORCPT ); Tue, 7 Jul 2009 11:56:59 -0400 Received: from gw1.cosmosbay.com ([212.99.114.194]:48390 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754614AbZGGP45 (ORCPT ); Tue, 7 Jul 2009 11:56:57 -0400 Message-ID: <4A537033.7060000@gmail.com> Date: Tue, 07 Jul 2009 17:56:35 +0200 From: Eric Dumazet User-Agent: Thunderbird 2.0.0.22 (Windows/20090605) MIME-Version: 1.0 To: Jiri Olsa CC: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, fbl@redhat.com, nhorman@redhat.com, davem@redhat.com, htejun@gmail.com, jarkao2@gmail.com, oleg@redhat.com, davidel@xmailserver.org Subject: Re: [PATCHv5 1/2] net: adding memory barrier to the poll and receive callbacks References: <20090703081219.GE2902@jolsa.lab.eng.brq.redhat.com> <20090703081325.GF2902@jolsa.lab.eng.brq.redhat.com> In-Reply-To: <20090703081325.GF2902@jolsa.lab.eng.brq.redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-1.6 (gw1.cosmosbay.com [0.0.0.0]); Tue, 07 Jul 2009 17:56:35 +0200 (CEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 13109 Lines: 370 Jiri Olsa a ?crit : > Adding memory barrier after the poll_wait function, paired with > receive callbacks. Adding fuctions sk_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 > > wbr, > jirka > > > Signed-off-by: Jiri Olsa Signed-off-by: Eric Dumazet > > --- > include/net/sock.h | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++ > 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 +++--- > 10 files changed, 85 insertions(+), 19 deletions(-) > > diff --git a/include/net/sock.h b/include/net/sock.h > index 352f06b..4eb8409 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -54,6 +54,7 @@ > > #include > #include > +#include > > #include > #include > @@ -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 > 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 7870a53..9114524 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/