From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753226Ab3ISSHa (ORCPT ); Thu, 19 Sep 2013 14:07:30 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:61820 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751689Ab3ISSH3 (ORCPT ); Thu, 19 Sep 2013 14:07:29 -0400 From: Will Deacon To: linux-kernel@vger.kernel.org Cc: torvalds@linux-foundation.org, Will Deacon , Waiman Long Subject: [PATCH] lockref: use cmpxchg64 explicitly for lockless updates Date: Thu, 19 Sep 2013 19:06:46 +0100 Message-Id: <1379614006-3844-1-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 1.8.2.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The cmpxchg() function tends not to support 64-bit arguments on 32-bit architectures. This could be either due to use of unsigned long arguments (like on ARM) or lack of instruction support (cmpxchgq on x86). However, these architectures may implement a specific cmpxchg64() function to provide 64-bit cmpxchg support instead. Since the lockref code requires a 64-bit cmpxchg and relies on the architecture selecting ARCH_USE_CMPXCHG_LOCKREF, move to using cmpxchg64 instead of cmpxchg and allow 32-bit architectures to make use of the lockless lockref implementation. Cc: Waiman Long Signed-off-by: Will Deacon --- An alternative to this patch is to go through the 32-bit architectures that implement cmpxchg64, reworking their cmpxchg definitions to switch to the 64-bit version based on the sizeof the argument. lib/lockref.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/lib/lockref.c b/lib/lockref.c index e2cd2c0..677d036 100644 --- a/lib/lockref.c +++ b/lib/lockref.c @@ -14,8 +14,8 @@ while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \ struct lockref new = old, prev = old; \ CODE \ - old.lock_count = cmpxchg(&lockref->lock_count, \ - old.lock_count, new.lock_count); \ + old.lock_count = cmpxchg64(&lockref->lock_count, \ + old.lock_count, new.lock_count); \ if (likely(old.lock_count == prev.lock_count)) { \ SUCCESS; \ } \ -- 1.8.2.2