From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932578AbcIAKUO (ORCPT ); Thu, 1 Sep 2016 06:20:14 -0400 Received: from foss.arm.com ([217.140.101.70]:54494 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932550AbcIAKUM (ORCPT ); Thu, 1 Sep 2016 06:20:12 -0400 Date: Thu, 1 Sep 2016 11:20:07 +0100 From: Catalin Marinas To: Vladimir Murzin Cc: Kenneth Lee , Will Deacon , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] [bugfix] replace unnessary ldax with common ldr Message-ID: <20160901102006.ye5uhbhwyqijgxvc@localhost> References: <1472538931-145463-1-git-send-email-liguozhu@hisilicon.com> <20160830090721.GC5163@e104818-lin.cambridge.arm.com> <57C6DC00.2050709@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <57C6DC00.2050709@arm.com> User-Agent: NeoMutt/ (1.7.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 31, 2016 at 02:30:40PM +0100, Vladimir Murzin wrote: > On 30/08/16 10:07, Catalin Marinas wrote: > > On Tue, Aug 30, 2016 at 02:35:31PM +0800, Kenneth Lee wrote: > >> (add comment for the previous mail, sorry for the duplication) > >> > >> There is no store_ex pairing with this load_ex. It is not necessary and > >> gave wrong hint to the cache system. > >> > >> Signed-off-by: Kenneth Lee > >> --- > >> arch/arm64/include/asm/spinlock.h | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h > >> index c85e96d..3334c4f 100644 > >> --- a/arch/arm64/include/asm/spinlock.h > >> +++ b/arch/arm64/include/asm/spinlock.h > >> @@ -63,7 +63,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) > >> */ > >> " sevl\n" > >> "2: wfe\n" > >> -" ldaxrh %w2, %4\n" > >> +" ldrh %w2, %4\n" > >> " eor %w1, %w2, %w0, lsr #16\n" > >> " cbnz %w1, 2b\n" > >> /* We got the lock. Critical section starts here. */ > > > > This is needed because the arch_spin_unlock() code only uses an STLR > > without an explicit SEV (like we have on AArch32). An event is > > automatically generated when the exclusive monitor is cleared by STLR. > > But without setting it with a load exclusive in arch_spin_lock() (even > > though it does not acquire the lock), there won't be anything to clear, > > hence no event to be generated. In this case, the WFE would wait > > indefinitely. > > Maybe worth to add this as a comment, no? Yes, we just need to find someone to send a patch ;). -- Catalin