From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758536AbZGIE0j (ORCPT ); Thu, 9 Jul 2009 00:26:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754234AbZGIE03 (ORCPT ); Thu, 9 Jul 2009 00:26:29 -0400 Received: from gw1.cosmosbay.com ([212.99.114.194]:55142 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751739AbZGIE02 (ORCPT ); Thu, 9 Jul 2009 00:26:28 -0400 Message-ID: <4A557153.8000108@gmail.com> Date: Thu, 09 Jul 2009 06:25:55 +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, mathieu.desnoyers@polymtl.ca, mingo@elte.hu, a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org, fbl@redhat.com, nhorman@redhat.com, htejun@gmail.com, jarkao2@gmail.com, oleg@redhat.com, davidel@xmailserver.org, davem@davemloft.net Subject: Re: [PATCHv7 2/2] memory barrier: adding smp_mb__after_lock References: <20090708220717.GB2945@jolsa.redhat.com> <20090708221031.GD2945@jolsa.redhat.com> In-Reply-To: <20090708221031.GD2945@jolsa.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]); Thu, 09 Jul 2009 06:25:57 +0200 (CEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jiri Olsa a écrit : > Adding smp_mb__after_lock define to be used as a smp_mb call after > a lock. > > Making it nop for x86, since {read|write|spin}_lock() on x86 are > full memory barriers. > > wbr, > jirka > > > Signed-off-by: Jiri Olsa Signed-off-by: Eric Dumazet > --- > arch/x86/include/asm/spinlock.h | 4 ++++ > include/linux/spinlock.h | 5 +++++ > include/net/sock.h | 5 ++++- > 3 files changed, 13 insertions(+), 1 deletions(-) > > diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h > index b7e5db8..4e77853 100644 > --- a/arch/x86/include/asm/spinlock.h > +++ b/arch/x86/include/asm/spinlock.h > @@ -302,4 +302,8 @@ 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. */ > +static inline void smp_mb__after_lock(void) { } > +#define ARCH_HAS_SMP_MB_AFTER_LOCK > + > #endif /* _ASM_X86_SPINLOCK_H */ > diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h > index 252b245..4be57ab 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 ARCH_HAS_SMP_MB_AFTER_LOCK > +static inline void smp_mb__after_lock(void) { 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 4eb8409..2c0da92 100644 > --- a/include/net/sock.h > +++ b/include/net/sock.h > @@ -1271,6 +1271,9 @@ static inline int sk_has_allocations(const struct sock *sk) > * 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. > + * > + * The sk_has_sleeper is always called right after a call to read_lock, so we > + * can use smp_mb__after_lock barrier. > */ > static inline int sk_has_sleeper(struct sock *sk) > { > @@ -1280,7 +1283,7 @@ static inline int sk_has_sleeper(struct sock *sk) > * > * This memory barrier is paired in the sock_poll_wait. > */ > - smp_mb(); > + smp_mb__after_lock(); > return sk->sk_sleep && waitqueue_active(sk->sk_sleep); > } >