From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934300Ab1KCBj4 (ORCPT ); Wed, 2 Nov 2011 21:39:56 -0400 Received: from cantor2.suse.de ([195.135.220.15]:51102 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934287Ab1KCBjq (ORCPT ); Wed, 2 Nov 2011 21:39:46 -0400 X-Mailbox-Line: From gregkh@clark.kroah.org Wed Nov 2 15:27:40 2011 Message-Id: <20111102222740.239662657@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Wed, 02 Nov 2011 15:25:50 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Mikael Pettersson , "David S. Miller" Subject: [006/101] sparc32: unbreak arch_write_unlock() In-Reply-To: <20111102222755.GA10893@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.33-longterm review patch. If anyone has any objections, please let us know. ------------------ From: Mikael Pettersson commit 3f6aa0b113846a8628baa649af422cfc6fb1d786 upstream. The sparc32 version of arch_write_unlock() is just a plain assignment. Unfortunately this allows the compiler to schedule side-effects in a protected region to occur after the HW-level unlock, which is broken. E.g., the following trivial test case gets miscompiled: #include rwlock_t lock; int counter; void foo(void) { write_lock(&lock); ++counter; write_unlock(&lock); } Fixed by adding a compiler memory barrier to arch_write_unlock(). The sparc64 version combines the barrier and assignment into a single asm(), and implements the operation as a static inline, so that's what I did too. Compile-tested with sparc32_defconfig + CONFIG_SMP=y. Signed-off-by: Mikael Pettersson Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- arch/sparc/include/asm/spinlock_32.h | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) --- a/arch/sparc/include/asm/spinlock_32.h +++ b/arch/sparc/include/asm/spinlock_32.h @@ -130,6 +130,15 @@ static inline void arch_write_lock(arch_ *(volatile __u32 *)&lp->lock = ~0U; } +static void inline arch_write_unlock(arch_rwlock_t *lock) +{ + __asm__ __volatile__( +" st %%g0, [%0]" + : /* no outputs */ + : "r" (lock) + : "memory"); +} + static inline int arch_write_trylock(arch_rwlock_t *rw) { unsigned int val; @@ -174,8 +183,6 @@ static inline int __arch_read_trylock(ar res; \ }) -#define arch_write_unlock(rw) do { (rw)->lock = 0; } while(0) - #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock) #define arch_read_lock_flags(rw, flags) arch_read_lock(rw) #define arch_write_lock_flags(rw, flags) arch_write_lock(rw)