From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933711AbbELTBe (ORCPT ); Tue, 12 May 2015 15:01:34 -0400 Received: from www.linutronix.de ([62.245.132.108]:56838 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753607AbbELTBC (ORCPT ); Tue, 12 May 2015 15:01:02 -0400 Date: Tue, 12 May 2015 21:00:14 +0200 From: Sebastian Andrzej Siewior To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, yang.shi@windriver.com, benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, heiko.carstens@de.ibm.com, schwidefsky@de.ibm.com, borntraeger@de.ibm.com, mst@redhat.com, tglx@linutronix.de, David.Laight@ACULAB.COM, hughd@google.com, hocko@suse.cz, ralf@linux-mips.org, herbert@gondor.apana.org.au, linux@arm.linux.org.uk, airlied@linux.ie, daniel.vetter@intel.com, linux-mm@kvack.org, linux-arch@vger.kernel.org, peterz@infradead.org Subject: Re: [PATCH v1 11/15] arm/futex: UP futex_atomic_op_inuser() relies on disabled preemption Message-ID: <20150512190014.GD25464@linutronix.de> References: <1431359540-32227-1-git-send-email-dahi@linux.vnet.ibm.com> <1431359540-32227-12-git-send-email-dahi@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1431359540-32227-12-git-send-email-dahi@linux.vnet.ibm.com> X-Key-Id: 2A8CF5D1 X-Key-Fingerprint: 6425 4695 FFF0 AA44 66CC 19E6 7B96 E816 2A8C F5D1 User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * David Hildenbrand | 2015-05-11 17:52:16 [+0200]: >The !CONFIG_SMP implementation of futex_atomic_op_inuser() seems to rely >on disabled preemption to guarantee mutual exclusion. Yes, this is what the code looks like. It is more the requirement for ldrex/strex opcodes which are ARMv6+ and so is SMP support (here). Documentation wise you could replace CONFIG_SMP by __LINUX_ARM_ARCH__ >= 6 in a later patch if you like. This would be more in-sync with arch/arm/include/asm/cmpxchg.h :) Sebastian