Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758889AbZFYPjW (ORCPT ); Thu, 25 Jun 2009 11:39:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757718AbZFYPjL (ORCPT ); Thu, 25 Jun 2009 11:39:11 -0400 Received: from mx2.redhat.com ([66.187.237.31]:55267 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756970AbZFYPjJ (ORCPT ); Thu, 25 Jun 2009 11:39:09 -0400 Date: Thu, 25 Jun 2009 14:24:29 +0200 From: Oleg Nesterov To: Jiri Olsa Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, fbl@redhat.com, nhorman@redhat.com, davem@redhat.com, eric.dumazet@gmail.com, Tejun Heo , Davide Libenzi Subject: Re: [PATCH] net: fix race in the receive/select Message-ID: <20090625122416.GA23613@redhat.com> References: <20090625122545.GA3625@jolsa.lab.eng.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090625122545.GA3625@jolsa.lab.eng.brq.redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9367 Lines: 252 Can't really comment this patch, except this all looks reasonable to me. Add more CCs. On 06/25, Jiri Olsa wrote: > > Adding memory barrier to the __pollwait function paired with > receive callbacks. The smp_mb__after_lock define is added, > since {read|write|spin}_lock() on x86 are full memory barriers. > > 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. > > wbr, > jirka > > > Signed-off-by: Jiri Olsa > > --- > arch/x86/include/asm/spinlock.h | 3 +++ > fs/select.c | 4 ++++ > include/linux/spinlock.h | 5 +++++ > include/net/sock.h | 18 ++++++++++++++++++ > net/atm/common.c | 4 ++-- > net/core/sock.c | 8 ++++---- > net/dccp/output.c | 2 +- > net/iucv/af_iucv.c | 2 +- > net/rxrpc/af_rxrpc.c | 2 +- > net/unix/af_unix.c | 2 +- > 10 files changed, 40 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h > index b7e5db8..39ecc5f 100644 > --- a/arch/x86/include/asm/spinlock.h > +++ b/arch/x86/include/asm/spinlock.h > @@ -302,4 +302,7 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw) > #define _raw_read_relax(lock) cpu_relax() > #define _raw_write_relax(lock) cpu_relax() > > +/* The {read|write|spin}_lock() on x86 are full memory barriers. */ > +#define smp_mb__after_lock() do { } while (0) > + > #endif /* _ASM_X86_SPINLOCK_H */ > diff --git a/fs/select.c b/fs/select.c > index d870237..c4bd5f0 100644 > --- a/fs/select.c > +++ b/fs/select.c > @@ -219,6 +219,10 @@ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address, > init_waitqueue_func_entry(&entry->wait, pollwake); > entry->wait.private = pwq; > add_wait_queue(wait_address, &entry->wait); > + > + /* This memory barrier is paired with the smp_mb__after_lock > + * in the sk_has_sleeper. */ > + smp_mb(); > } > > int poll_schedule_timeout(struct poll_wqueues *pwq, int state, > diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h > index 252b245..ae053bd 100644 > --- a/include/linux/spinlock.h > +++ b/include/linux/spinlock.h > @@ -132,6 +132,11 @@ do { \ > #endif /*__raw_spin_is_contended*/ > #endif > > +/* The lock does not imply full memory barrier. */ > +#ifndef smp_mb__after_lock > +#define smp_mb__after_lock() smp_mb() > +#endif > + > /** > * spin_unlock_wait - wait until the spinlock gets unlocked > * @lock: the spinlock in question. > diff --git a/include/net/sock.h b/include/net/sock.h > index 352f06b..7fbb143 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -1241,6 +1241,24 @@ 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 __pollwait. > + */ > + smp_mb__after_lock(); > + return sk->sk_sleep && waitqueue_active(sk->sk_sleep); > +} > + > /* > * 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..67a8642 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); > 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/iucv/af_iucv.c b/net/iucv/af_iucv.c > index 6be5f92..ba0149d 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); > diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c > index eac5e7b..60e0e38 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); > } > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c > index 36d4e44..143143a 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); > } -- 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/