From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752281Ab1HOL1N (ORCPT ); Mon, 15 Aug 2011 07:27:13 -0400 Received: from fanny.its.uu.se ([130.238.4.241]:10912 "EHLO fanny.its.uu.se" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751634Ab1HOL1K (ORCPT ); Mon, 15 Aug 2011 07:27:10 -0400 X-Greylist: delayed 1078 seconds by postgrey-1.27 at vger.kernel.org; Mon, 15 Aug 2011 07:27:10 EDT MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <20040.65109.439941.444670@pilspetsen.it.uu.se> Date: Mon, 15 Aug 2011 13:09:09 +0200 From: Mikael Pettersson To: sparclinux@vger.kernel.org Subject: [PATCH,SPARC] make sparc32 arch_write_unlock() match the sparc64 version Cc: linux-kernel@vger.kernel.org X-Mailer: VM 7.17 under Emacs 20.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(), so that's what I did here as well. Compiled-tested with a sparc32 SMP kernel. Signed-off-by: Mikael Pettersson --- --- linux-3.1-rc2/arch/sparc/include/asm/spinlock_32.h.~1~ 2011-07-22 12:01:08.000000000 +0200 +++ linux-3.1-rc2/arch/sparc/include/asm/spinlock_32.h 2011-08-15 11:43:49.000000000 +0200 @@ -131,6 +131,15 @@ 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; @@ -175,7 +184,7 @@ static inline int __arch_read_trylock(ar res; \ }) -#define arch_write_unlock(rw) do { (rw)->lock = 0; } while(0) +#define arch_write_unlock(rw) arch_write_unlock(rw) #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock) #define arch_read_lock_flags(rw, flags) arch_read_lock(rw)