From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751489AbeCZKiC (ORCPT ); Mon, 26 Mar 2018 06:38:02 -0400 Received: from mail-wr0-f193.google.com ([209.85.128.193]:38790 "EHLO mail-wr0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751076AbeCZKiB (ORCPT ); Mon, 26 Mar 2018 06:38:01 -0400 X-Google-Smtp-Source: AG47ELsdG80W4cHTiX6wG30ULZmPhf8iaDj+Eb2ilIWvqbHDe1SEKHyPuQWZFB89hbZTf71nN4j4xw== From: Andrea Parri To: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Peter Zijlstra , Ingo Molnar Cc: linux-kernel@vger.kernel.org, Andrea Parri , Linus Torvalds Subject: [PATCH for-4.17 2/2] powerpc: Remove smp_mb() from arch_spin_is_locked() Date: Mon, 26 Mar 2018 12:37:47 +0200 Message-Id: <1522060667-7034-1-git-send-email-andrea.parri@amarulasolutions.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 51d7d5205d338 ("powerpc: Add smp_mb() to arch_spin_is_locked()") added an smp_mb() to arch_spin_is_locked(), in order to ensure that Thread 0 Thread 1 spin_lock(A); spin_lock(B); r0 = spin_is_locked(B) r1 = spin_is_locked(A); never ends up with r0 = r1 = 0, and reported one example (in ipc/sem.c) relying on such guarantee. It's however understood (and undocumented) that spin_is_locked() is not required to ensure such ordering guarantee, guarantee that is currently _not_ provided by all implementations/arch, and that callers relying on such ordering should instead use suitable memory barriers before acting on the result of spin_is_locked(). Following a recent auditing[1] of the callers of {,raw_}spin_is_locked() revealing that none of them are relying on this guarantee anymore, this commit removes the leading smp_mb() from the primitive thus effectively reverting 51d7d5205d338. [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 Signed-off-by: Andrea Parri Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michael Ellerman Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Linus Torvalds --- arch/powerpc/include/asm/spinlock.h | 1 - 1 file changed, 1 deletion(-) diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h index b9ebc3085fb79..ecc141e3f1a73 100644 --- a/arch/powerpc/include/asm/spinlock.h +++ b/arch/powerpc/include/asm/spinlock.h @@ -67,7 +67,6 @@ static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock) static inline int arch_spin_is_locked(arch_spinlock_t *lock) { - smp_mb(); return !arch_spin_value_unlocked(*lock); } -- 2.7.4